Abstract: The 17Cr2Ni2Mo steel specimens were surface strengthened by single steel shot peening and composite shot peening with steel shot and ceramic shot. The residual stress, residual austenite content and micro hardness distribution along the depth direction on the surface of the steel after shot peening strengthening were tested. And the surface shot peening strengthening parameters were optimized. The results show that the steel after composite shot peening had higher surface residual stress and maximum residual stress than those after single shot peening. The former had deeper maximum depth in which the residual austenite transformed to martensite than the latter. And the former had higher surface hardness and better strengthening effect than the latter.