Abstract: The critical phase transformation point and thermal expansion curve of 3Cr2MnNiMoV steel with different content of Mo was obtained by FORMASTOR-FⅡ phase transformation tester. Combining with the results of microstructure and hardness, the austenite continuous cooling transformation (CCT) curve was drawn. The effect of Mo content on the austenite continuous cooling transformation behavior of the tested steel was studied. The results show that when the cooling rates was 0.03-16.2℃·s^-1, CCT curves of the test steels were both divided into medium temperature transformation zone and low temperature transformation zone, and the phase transformation products were bainite and martensite, respectively. The pearlite was not found. With the increase of Mo content, the critical cooling rate of martensitic transformation decreased, the CCT curve shifted to the right and the hardenability increased. With the increase of cooling rates, the micro-hardness of the tested steel increased slowly and then rapidly. When the cooling rate was larger than 0.14℃·s^-1, the tested steel containing more Mo element had higher hardness under the same cooling rate.