In this paper, Content of carbon and alloy element, morphology of martensite both in inside and surpace,and Their affects on properties,which emerge in CD carbured and quenched Crl2MoV steel, are studied by means of TEM and SEM. The observation reveals, although Cr12MoV steel containes high content of carbon and was carburized,both in outside and inside micro.structure exists only multi-martensite, in which dislocation martensite is dominant.The carburized layer is composed of this typo of martensite, retained austenite as well as dispersed fine carbide, which contributes stength and toughness.