Abstract: The effects of austenitizing and tempering temperature on the microstructure and mechanical properties of powder metallurgy high speed steel (PMHSS) S390 were investigated. The results reveal that the microstructure of martensite, retained austenite and alloy carbide could be obtained in the samples high-pressure vacuum gas quenched (0.6 MPa) and oil quenched after austenitizing at 1 190, 1 230 ℃, the microstructure became fine alloy carbide and tempered martensite after high temperature tempering for three times. Moreover, the secondary hardening effect of S390 steel was obvious, and the peak of secondary hardening was at 500 ℃ and 540 ℃ for samples after high-pressure vacuum gas quenching and oil quenching. The hardness and compressive strength were 67.2 HRC and above 3 862 MPa, when the S390 steel was experienced the optimal process, oil quenching at 1 230 ℃ and two-hour tempering at 540 ℃ twice then at 510 ℃ once.