Abstract: The statically indeterminate problem for tension and compression is one of the difficulties in the teaching of mechanics of materials. The key point is to establish the supplementary equation of deformation compatibility. The small deformation magnification graph is usually used in existing text books to build the equations, which are problem-dependent and hard to be mastered. A method using the compatibility condition of nodal displacements and their relationships between the axial deformation of bars is presented. The theory of the method is introduced and three examples are given to demonstrate the implementation process. Compared with the traditional method, the present method is easy to be mastered and can be used as a general method for establishing the compatibility condition of deformations.