Abstract: The accuracy of concept description needs to be emphasized in the course of mechanics of materials. In this paper, several concepts in mechanics of materials are discussed. At present, the descriptions about internal force components on a cross-section and torsional deformation are only suitable for the case that the cross section has two or more than two symmetrical axes. More accurate descriptions are proposed in this paper. The difference between beam deflection and deformation is emphasized, and it is proposed that the overall deformation of beams is described by the integral term (first term) in the equation of deflection curve. In the analysis of combined compression and bending and in the analysis of stability of column, different treatments about the additional bending moment generated by axial force under bending deformation reflects the inherent connection between two knowledge points and the flexible of mechanical modeling.