This article describes the research of plastic deformation of ferrite steel, ferrite-pearlite steel and quench-tempered steel during tensile and fatigue tests by transmission electron microscopy (TEM). The dislocation tangle model of interaction between dislocations and carbides, the propagation modes of wide fatigue deformation band for initiation of fatigue crack and the competitive model of microscopic cyclic hardening and softening during fatigue test are discussed in detail