The invention discloses a block model building method for complex geological structure, and relates to the geological field of three-dimension modeling comprising the following steps: a, triangular meshing description is carried out on planes or fault planes; b, after step a, level intersection in block modeling for complex geological structure is converted into triangle intersection in space, whether the two triangles are intersected is judged, points of intersection are found from the two intersected triangles, and a line of intersection is obtained by connecting the points of intersection; c, geometric consistency and topological consistency are carried out on inside of each intersected triangle; d, after step c, enclosing block is extracted to obtain an interface formed by peripheral sides of the enclosing block, and is defined geological attribute to form three dimension model block. The method in the invention completely solves the problems of three dimension model input and blocking in complex geological regions, avoids using equations set with high solving difficulty and calculated amount, and is simple and practical.