Abstract: The tensile test and creep tests under different stresses of 9Cr-1.5W steel with silicon mass fractions of 0.34%, 0.60% and 0.90% were carried out at 550 ℃. The effect of silicon content on tensile and creep properties of the test steel at high temperatures was studied. The results show that with the increase of silicon content, the yield strength and tensile strength of the test steel at 550 ℃ decreased, the percentage elongation after fracture increased, and the strain hardening index increased first and then decreased. The test steel with 0.60wt% silicon had the largest strain hardening index. The test steel with 0.60wt% silicon had a long creep time under different stresses, and exhibited the best high temperature creep performance, the lowest stress index, and the lowest minimum creep rate sensitivity to applied stress. The creep behavior of the test steel was controlled by dislocation climbing.