In 1381, Lan Yu was appointed "Left Deputy General Who Conquers the South" () and accompanied Fu Youde to attack Yunnan and pacify the region. He was rewarded with 500 "dan" of grain and his daughter was granted the title of "Princess Consort of Shu" (). In 1387, Nahachu () of the Northern Yuan invaded Liaodong and the Hongwu Emperor sent Feng Sheng, with Lan Yu and Fu Youde as his right and left deputies respectively, along with a 200,000-man army to attack him. Nahachu was defeated and surrendered. Lan Yu garrisoned the army at Jizhou ().