Abstract: The microscopic structures and inclusion in 42CrMoV bolt were investigated by SEM,STEM and software ASPEX. The results show that the matrix structure of 42CrMoV bolt is tempered sorbite,but still retains the original morphology of martensite. Carbides precipitate and arrange orderly in intracrystalline and lath boundaries,and the amount of precipitated carbides in grain boundaries are more than that in intracrystalline. Besides,the micro-hardness HV0.2 is 330 and the grain size(level) of austenitic is 9. The Mn S and aluminate are the main inclusion types in 42CrMoV bolt,and the size of inclusions are mostly less than 5 μm,the level of A,B,C,D and Ds inclusion was basically less than or equal to Level 0.5.