This paper explains the forward and inversion methods, which include ray-tracing based on the shortest path ray-tracing method and inversion calculation based on LSQR. The authors made detailed researches on the two algorithms, rebuilt the original image of underground structures, with fairly good effect obtained. Exemplified by engineering application, the results indicate that cross-hole seismic tomography can reflect underground conditions and also provide more concrete data for the study of geological structure and final-period construction. The resolution of the cross-hole seismic tomography is discussed, and the factors affecting the image quality are indicated.