Lan Yu (died 22 March 1393) was a Chinese military leader and one of the most influential generals of the Hongwu Emperor, the founder and first emperor of the Ming dynasty. His exceptional military skills and the support of his relative, Chang Yuchun, earned him a high-ranking position in the Ming army. Throughout the 1380s, he rose to prominence as one of the empire's top military leaders. In 1393, he was accused of conspiracy and attempted coup, leading to his downfall and execution. His family and a large number of his relatives and subordinates were also executed, resulting in the deaths of thousands of people during the purge.

Lan Yu was from Dingyuan in Anhui Province. In the 1360s, his elder sister married Chang Yuchun, the second most important general of Zhu Yuanzhang, who was establishing his own state during the Red Turban Rebellion against the Mongol-led Yuan dynasty. Lan served as an officer in Chang's army and quickly rose through the ranks during this period.

By 1371, Lan had become a general in Fu Youde's army, which was tasked with conquering Sichuan under the Hongwu Emperor's orders. The following year, Lan was transferred to the army of Xu Da, which marched north from Shanxi to confront Mongol warlord Köke Temür. In April 1372, Lan led a separate force and defeated Köke Temür at the Tula River. He then continued to serve in the north, leading an expedition against the Mongols gathered north of Kalgan in 1374. In 1375, Lan played a role in the defense of Yan'an against the Mongols.

In November 1378, the Emperor appointed Lan as Mu Ying's deputy in the campaign against the Tibetans in Gansu. In October 1379, the Tibetans suffered a defeat, and the Ming generals returned to the capital. In December 1379, the Emperor awarded twelve of them noble titles. Most of these generals were later executed as members of Lan's conspiracy. Lan himself became the Marquis of Yongchang (永昌侯), with an annual income of 2,000 dan (about 119 tons) of grain.

In September 1381, Lan served as Fu's deputy during the Ming conquest of Yunnan. In January 1382, after Ming troops defeated the Yuan army in the first phase of the campaign, Lan led a separate detachment to Dali and conquered it, gaining control of northwestern Yunnan. The Emperor awarded Lan by increasing his income to 2,500 dan and allowed his daughter to marry the Emperor's eleventh son, Zhu Chun, Prince of Shu.

In September 1385, Feng Sheng, along with his deputies Lan and Fu, assumed control of the army in Beijing. After thorough preparations, they were tasked with suppressing the Mongol forces in southern Manchuria in January 1387. Lan led the vanguard and defeated some of the Mongols. In July that year, the main Ming army defeated the enemy forces and captured their commander Naghachu. In September 1387, the Hongwu Emperor dismissed Feng due to his unsatisfactory performance during the campaign. Lan then took over as the commander of the army and established his headquarters east of Beijing. In November 1387, Lan was given the order to attack the main Mongol forces under Khan Tögüs Temür. By mid-May 1388, a massive army of 150,000 Ming troops had marched across the Gobi Desert into northeastern Mongolia. They took the Mongols by surprise at Buir Lake, located 500 miles (800 km) north of Beijing. Although Tögüs Temür fled the battle, Lan's troops were able to capture tens of thousands of prisoners and defeat the Mongol general Qarajang on their way back. Upon returning to Nanjing in September 1388, Lan and his subordinates were generously rewarded for their victory. On 19 January 1389, the Emperor granted Lan the title Duke of Liang (涼國公) with an annual income of 3,000 dan. This was a significant achievement, as he was only the third duke to be appointed since 1370. Lan was part of a new generation of generals who rose to prominence after the civil wars of the 1360s. The Emperor also compared Lan to Han general Wei Qing and Tang general Li Jing.

In March 1389, Lan was sent to Sichuan, and the following year he suppressed revolts in southwestern Huguang. Upon his return to Nanjing in September 1390, the Emperor increased his income to 3,500 dan. In April 1391, he sent Lan to Shaanxi with two other dukes and several marquises to command the frontier army.

In February 1392, the Emperor dismissed several influential generals from their commands, including Lan, Li Jinglong, and Chang Sheng. The Emperor had developed a distrust of the military elite as a whole, but Lan still retained his favor, despite his occasional tactless behavior. In March, Lan was sent to command the army in Lanzhou against the Mongols. In Sichuan, the commander of the Jianchang guard, Yelü Temür (月魯帖木兒), gained the support of local non-Chinese tribes and rebelled. The troops loyal to the Ming were unable to stop Yelü Temür, so Lan and his army were sent to confront him. Before his arrival, the loyalists defeated the rebels in July 1392 and captured their commander by the end of the year. In order to prevent future rebellions, Lan proposed relocating a larger number of soldier-peasants to Sichuan. This recommendation came at a time when the government faced the issue of soldiers being abused by their commanders. The Emperor, angered by this issue, used it as a pretext to recall Lan to Nanjing in December 1392.