The direction of contact force is uncertain in dealing with corner-corner contact when the traditional discrete element numerical methods are used. At the same time the contact force calculation in three dimensions is extremely complex. Contact force calculation method based on potential proposed by Munjiza is a good solution to this problem. But the physical meaning of the potential is not clear. The calculated contact force does not match the physical intuition when embedding capacity is the same and the contact force is different. A new potential contact force calculation method is proposed using a unified calibration. The method redefines the potential function as the potential of a point in triangular proportional to the shortest distance from the point to the three sides of the triangular. This potential function definition can characterize the embedded amount in a unified way. When the embedding capacity is same, the calculated contact force is same, while all the advantages of the contact force with the potential can be kept. This redefined potential function overcomes the significant deficiencies of the original potential function. As long as the overlapping areas are constant, the total calculated contact force would be the same. The contact force calculation has local features, regardless of the overall shape and size of triangular element. The new contact force calculation method has better robustness grid. The method enables the contact force calculation with potential methods to build on a solid foundation of physics, which is significant.