;In the early Ming Dynasty, for the defense of Mongolians invasion, the government set up nine defensive area in the northern frontier. Yongle abolished Daning and Dongshengwei, then the scope of control of northwestern territory of the Ming government was limited to the Yellow River- Hetao Area inside, which made the Hetao Area exposed directly to the Mongolians armies. Since Dongshengwei was abolished, Yansui defensive area became the first line of northwestern territory defense affairs.
After the battle of Tumu, the border defense policy was changed from active to passive . From the Chenghua period, it had been advised by officials to move Sueidezhen to Yansui/Yulinwei?, and began to propose to build walls to resist Mongolians’ violations. The reason for the unsuccessful recover Hetao Area were concluded as dry climate, heavy logistics, and declining military strength, and harassment of the Mongolians etc. However, the construction of the wall can not stop the Mongolian breakthroughs in Yansui and Huama Pool, and robbing people over there.
In the study we discuss the influence of the abolition of Dongshengwei from Yansui defensive area, and the Ming government′s control over the Hetao Area in the middle of the dynasty in Chenghua to Hongzhi (1465-1505), also study the construction and geographical location of Defensive Area Yansui. It also studies the construction of the wall of Huamachi to Defensive Area Yansui, the impact of natural disasters on Shaanxi, the purveyance and logistics there, and the management of horses. By the discuss of Yansui defensive area, the study intend to know why the Hetao abandonment, and the defense of the wall had became a feasible method in that era.