Abstract: The swelling capacity in high vanadium high speed steel after austenitizing at 1 000 ℃ and at different cooling rates was tested using a Gleeble 1500D thermal simulation testing machine.The expansion curves of phase transformation and the continuous cooling transformation (CCT) curves have been drawn by Origin software.The results show that the transformation of perlite,bainite and martensite occurre in the continuous cooling process.Perlite,bainite,martensite and residual austenite could be obtained at the cooling rate of 0.25 ℃/s.The critical cooling rate of the steel is 0.5 ℃/s.The martensite start transformation Ms is lower than 200 ℃ and decreases with the increase of cooling rate.