The basic theory of extension method is introduced and the method is applied into risk zoning of geological disaster. Eight evaluation indexes were selected to be synthesis appraising system; they are the number of the existed geological diseases

the objects involved by the diseases

the lithology and the weathering degree of the rock mass

the relation between the dip of the discontinuities and the strike of the slopes

the features of the fractures

the influence intensity of human activities

the hydrogeolgy conditions and the dip angle of the slope surface. The risk grading standard is established; and corresponding value assignment is done. During the process of evaluation

the square of 100×100 m2 grid on geographical map is designed as the basic assessment element

and the corresponding zoning grade is obtained by means of grid data processing through computer program. The practical situation of the evaluation area is exactly reflected from the characteristic value of grade. The application practice proves that the extenics method is feasible in risk zoning of geological disaster in Xiangjiahe Bridge bank of Three Gorges Reservoir area in Zhongxian County of Chongqing.