Abstract: The dynamic fracture toughness ,tensile strength and plasticity of stream-turbine cylinder body steel on the different condition ( no aging ,593 ℃ aging 5 600 h) were studied by impact test-instrumented test method and tensile test method . The result was obtained. At different testing temperatures ,compared with no aging and after aging,the dynamic fracture toughness and the side-swell value of fracture were both decreased,the tensile strength increased in some sort and the plasticity decreased a little. The result from SEM analysis and the method of phase analysis by physics and chemistry was obtained. A small amount of carbide was precipitated from intracrystalline and intergranular of aging sample.And this was mostly because micro phase of M23C6 containing Cr was precipitated dispersedly from matrix.Some carbide particles became gathered and growing after aging,and the mean particle size of second-phase of aging sample became enlarged in some sort.