Martensite heat resistant steel 1Cr20Co6Ni2WMoV was melted by a vacuum induction fumace with 22.5 kg ingot and forged to 中16 mm bar.Heat treatment process of samples were quenching at 1060 ℃ for 1h oil cooling + cold treatment at -70℃ or- 192 ℃ for 2 h air cooling + tempering at 640 ℃ for 3 h air cooling. Test results showed that with both heat treatment process the structure of steel   1Cr20Co6Ni2WMoV  consisted of high density dislocation tempering lath martensite

residual austenite

δ- ferite and M

23

C

6

.With cold treatment temperature decreased from -70 ℃ to - 192 ℃ the amount of M

23

C

6

precipitated at grain boundary and the dislocation density in grain inside increased

the a- mount of residual austenite decreased and the tensile and yield strength of steel respectively increased from 1045

MPa and 715 MPa to 1090 Mpa and 760 MPa.