Abstract: The propagation prediction for mobile communication base station is the key problem for the design of mobile communication network. The ray-tracing method is an efficient tool to resolve the problem. Now the ray-tracing researches are mostly concentrated in the direct algorithms. Only a few papers treat about the inverse algorithms, in spite of the more accuracy of inverse algorithms. Because the implementation process is very complicated. The wedge of building can be divided into vertical wedge and horizontal wedge. This paper discusses in detail the vertical wedge diffraction algorithms of inverse ray-tracing method.First, it uses the scanning algorithm to get the visible wedge table, then identifies the effective propagation path, calculates the receiver field strength of each path and accumulates to get the total diffraction field strength. Finally, verify the method through a cell model.