Abstract: A block model constructing method for complex geological structures is provided. The method comprises the following steps: a) making a triangle mesh description of a layer plane or a fault plane; b) judging whether two triangles intersect, and finding out the intersection points if they intersect; c) performing a geometric consistency and topological consistency processing within every intersectant triangle; d) extracting an enclosing block to acquire an interface constituted of peripheral edges of the enclosing block, and defining a geological attribute of the enclosing block to form a three-dimensional model block. The method needs not to solve difficult equation sets with large computation, thus simplifying the constructing method.