With the entry of Great Britain and later the United States in the war against Japan, he was transferred to southern China as commander of the Nationalist Chinese XI Group Army.

Y-Force consisted of over 100,000 Nationalist soldiers, and participated in major ground operations in support of American General Joseph W. Stilwell's offensive in northern Burma.

In concert with existing airlift operations over The Hump, the Ledo Road enabled overland transport of military supplies from Assam to Nationalist bases in China.

After being cut off from land communication with the KMT with the communist capture of Chinchow, Liaoning, he was supposedly planning for an offensive to recapture the Nationalist provincial capital before he was ordered to withdraw by Chiang Kai-shek.

Shortly before the communist capture of Mukden (Shenyang), Wei would return to southern China following his replacement by his field commander Du Yuming in October 1948.