Abstract: The cover system of the plane numerical manifold method (NMM) was discussed based on the mesh of the triangle finite element method (FEM). The numbers of physical cover of the cover system in NMM when the crack was extended were amended through the setting of hanging nodes. The formation methods of the numbers of physical cover, the hanging nodes and the angle notes of the integral area in the new manifold elements, when the crack was extended, were advanced through setting the chain list of the manifold elements only that were created when the original finite elements were disparted by physical mesh. Then the formation algorithm of the physical covers and the manifold elements in NMM were advanced when the crack was extended. The calculated result shows that the algorithm .is .feasible.