For any load the function from load is in multiplication shear force by antisymmetry load.

The bending deformation is one of the most important deformations in the engineering, analysis of internal bending forces is the key for knowing the bending deformation, the internal bending forces include two factors of the shear and bending moment, and to draw the internal bending force diagram is to draw the shear diagram and bending moment diagram.

The writer of this paper uses a new method called“tracking slope method”todraw a shear diagram and a bending moment diagram in the classroom teaching of mechanics ofmaterials.

Through the study of the calculous relation of external load and internal force,the exocentric rule has been found about shear diagram and blending moment.

We calculate their strength based on finding the critical section by drawing the shearing force diagram and bending moment diagram that is relatively complex and needs lots of work.

We calculate their strength based on finding the critical section by drawing the shearing force diagram and bending moment diagram , that is relatively comp lex and needs lots of work.

This paper expatiates on applying EXCEL in cultivating initial force of plane beam and drawing,the way of cultivating the initial force of plane beam under three familiar loads and drawing relative shear force diagram and bending moment diagram,which is of practical value in teaching,research and engineering practice.