Abstract: Taking two economic martensitic stainless steels with different chemical compositions as the research objects,the influences by the contents of C and Cr on the physiochemical properties of the economic 13Cr steel are studied by means of simulation test with quenching phase transformation instrument and the microanalysis. The result reveals that The austenite transformation starting temperature and ending temperature of Steel A are higher than those of Steel B by 26℃and 11 ℃separately,due to the fact that the higher C content causes the higher super saturation of the matrix Atom C,and relatively more carbide precipitation,and thus stronger thermodynamic conditions drive are needed to complete the austenitization;and the martenitic transformation temperature of Steel B is higher than that of Steel A,because the relatively low C content gets the martentic transformation shear resistance reduced. Finally provided here are the optimal austenitization temperatures of the above mentioned two steels,and the heat treatment processes as meeting the requirements for the mechanical properties of the casing in St. G. 110.