Abstract: Voronoi diagram is a basic data structure about space partitioning. Taking Xichang city and Tianjin coastal area as an example, this paper defines the influence range of each borehole by using Voronoi diagram, and finally divides the boundary of different types of site classification. This solved the problem of the number of holes and the artificial division of the subjective, and intuitively reflects regional boundary conditions. The study is a beneficial attempt of the using of the Voronoi diagram in engineering seismology site classification, and provides a new way of thinking for the area of site classification, at the same time, it provides an semi-quantitative reference for the area of regional seismic planning and seismic fortification.