Based on the theory of computer graphics concerned with the OpenGL,the key techniques of implementation of some functions such as STL preview,STL assembly and STL adjustment in pre-process module of foundry CAE system were investigated,including reading and writing of STL file,drawing of triangular facet,drawing of mold model with transparent effects,three-dimensional coordinate transformation of the whole mold system and calculation of normal vector of triangular facet,etc.A grap-handling program with the techniques mentioned above was developed and incorporated into the CAE system self-developed.The application of the system shows that those techniques are much contributive to making a reasonal plan of mesh generation.