Virtual hand grasping rules are interaction rules for a virtual hand and the virtual object to perform grasping operations. It’s used to determine whether the virtual hand can successfully grasp the object. We study geometrybased virtual hand grasping rules and physicsbased virtual hand grasping rules respectively. The former rules are simple but the simulation effect is poor. The latter rules are complicated to calculate and difficult to implement real-time simulations. In view of the above problems,  (1) we improve geometry-based virtual hand grasping rules, and formulate the gripping rules by the contact point position, the normal vector and the gripping’s surface normal vector to make the effect approach to force closure virtual hand grasping rules; (2) based on the invariability characteristic of the closed contact point and the normal vector in the force closure calculation, we avoid the nonlinear programming solution in the grasping operation by the internal force ratio, and realize real-time simulations in the grasping operation stage; (3) through the strategy of “initial grasping judgment based on geometric constraintforce closure calculation correction-internal force ratio for force closure calculation”, we realize  real-time simulations of complete grasping operation. We design interaction experiments to verify that the proposed grasping rule can achieve high immersion and real-time grasping simulations, and it can be applied to simulation platforms such as virtual training and virtual assembly.