Many important geometry and kinematics mechanism results about the Miyun—Xifengkou fault, which is an important east—west fault in the Yanshan area, have been achieved, but a significant divergence still exists in how the fault extend after arrived Xifengkou area. One view is that the eastward of the fault is consistently E—W and the whole fault is from west to east； the other view is that the extending towards northeast and the whole fault is a southeast protruding arcuate fault. There are different opinions on the problems of extension way and extending distance for each of the views. In this paper， one conclusion is obtained by analysing the aeromagnetic data and refering to the supplementary geological and satellite remote sensing image data that the Miyun—Xifengkou fault is obviously divided into two sections. The west section is from Miyun to Xifengkou, whose direction is from west to east; the other section is on the east of Xifengkou, which extends toward northeast and arrives at Tangdaohe (Kuancheng county) via Dongdadi (Kuancheng county) and Liangjiatai (Kuancheng county), and it is a southeast protruding arcuate fault in the whole.