Sun Yuanhua (1581 or 1582 – 7 September 1632), also known as Ignatius Sun, was a Chinese mandarin under the late Ming. A Catholic convert, he was a protégé of Paul Xu (né Xu Guangqi). Like his mentor, he advocated repelling the Manchu invasion by modernizing Chinese weaponry and wrote treatises on geometry and military science influenced by the Jesuits' European knowledge. From 1630 to 1632, he served as governor of Denglai, a Ming district around Dengzhou and Laizhou in northern Shandong. He was deposed by the mutiny of Kong Youde and Geng Zhongming, after which he was arrested and executed by the Ming for having failed to crush their rebellion with sufficient severity.

Sun Yuanhua initially went by the courtesy name Chuyang. Upon his conversion, he adopted the baptismal name Ignatius (Portuguese: Inácio) in honor of St Ignatius, the founder of the Jesuit order. He then adopted the courtesy name Huodong, which loosely translates it.

Sun was born in Jiading in the province of Southern Zhili (now within Shanghai) in 1581 or 1582 during the late Ming. He passed Southern Zhili's provincial exam and became a juren in 1612. Converting to Roman Catholicism under the influence of the Chinese Jesuit mission, he became a protégé of Paul Xu, who instructed him in western mathematics and use of firearms.

Sun joined Xu and his fellow converts Leo Li and Michael Yang in writing memorials supporting Christianity in response to the harshly condemnatory memorials published by Shen Que (沈㴶) in 1616 and 1617 after he became the vice-minister of the Department of Rites at Nanjing. In the end, the Wanli Emperor sided with Shen: A number of Chinese converts were jailed; Alphonso Vagnoni and Álvarõ de Semedo, the Jesuit leaders at Nanjing, were imprisoned and then expelled; and the Catholic buildings in Nanjing were demolished.

After the fall of Guangning (now Beizhen in Liaoning) to the Manchu, Sun Yuanhua published two memorials advocating the use of European-style cannon to defend the capital and the northeastern borders and passes. He argued that "at this stage the army is terrified of the enemy. If we are not under the shelter of garrisons, our condition will not be stable [and,] if we do not use telescopes and excellent cannon to strike first from a distance of 10 li or more, then the enemy will not be warded off." Most such military memorials were composed by mandarins unfamiliar with war and consisted of general platitudes and historical anecdotes, often dating back to the Zhou or earlier. Despite a general sense of cultural superiority and desire for self-sufficiency—evident in modern artillery becoming generally known as "red-barbarian cannon"—and although Sun failed Beijing's imperial examination for 1622, his memorials attracted important attention at the War Ministry because of the strength of his arguments and the great and familiar detail he included concerning the construction and use of modern cannon and fortifications. On 15 March 1622, the supervising censor Hou Zhenyang, working at the Office of Scrutiny for Personnel, composed a memorial lauding Sun's talent: "Sun Yuanhua... should be employed urgently to cast cannon and to construct garrisons... Let [him] investigate and measure the terrain, pin down the routes that should be followed, establish a platform [for cannon] at each juncture and then, with the cost of one platform as a base of reference for the others, the entrances to the passes will be rock-safe!... Let Yuanhua teach the tactics to the generals and commanders, [since] only the people who actually make the cannon can teach how to operate cannon." Hou was dismissed because of a memorial against Shen Que and the "Eunuch Party" but not before his proposals regarding Sun were put into practice. The war minister and grand secretary Sun Chengzong offered Sun Yuanhua a place on the ministry staff but acceded to his demands to take up responsibility in the war zone, making him a "military commissioner responsible for armament in the field". A general modernization program was delayed, however, when a 1623 demonstration of foreign artillery at Beijing went awry and a piece exploded, killing a Portuguese artillerist and three Chinese. Though subdued, official interest continued: Yuan Chonghuan began supporting Sun's policies in 1626.

An important meeting was held at Sun's Jiading estate around 1627, where Andrea Palmeiro, Xu, Sun, Yang, and eleven Jesuit missionaries planned the future of Christian expansion in China, including the status of Chinese rites and which Chinese name should be used for the Christian God.

Following Xu and Li's 1629 memorials, the Portuguese captain Gonçalo Teixeira Corrêa was permitted to bring ten artillery pieces and four "excellent bombards" across China to begin the training of Ming troops in European-style cannon. Further reinforcements were turned back at Nanchang in Jiangxi, owing to an outpouring of official complaints when a sudden illness removed the threat of a Manchu assault on Beijing. The merchants in Guangzhou were anxious lest their special monopolies on Portuguese trade be curtailed but a memorials of Lu Zhaolong singled Sun Yuanhua out for particular condemnation because of his overly fond treatment of the foreigners.

In 1630, Sun received the title of Shandong's Assistant Surveillance Commissioner for "having penetrated deep into the camp of the enemy". Liang Tingdong, the minister of war, offered him the post of governor of Denglai (t 登萊, s 登莱, Dēnglái) in northern Shandong, but Sun was hesitant. He composed a memorial stating