Abstract: A Z′-parameter method based on rate-temperature parameter (RTP) was proposed to be used in reliability analysis of the steady creep rate of new high strength aluminum alloy, where Z′parameter refers to the deviation of creep property from master curve. The steady rate data of creep experiments were studied to evaluate the distribution of Z′parameter. StressRTPreliability curves and temperatureallowable stressreliability curves were proposed for new high strength aluminum alloy based on Z′parameter in this paper. The results demonstrate that the scatter of Z′parameter for new high strength aluminum alloy is supported by normal distribution. As the reliability increases, the predicted upper limit of steady creep rate raises. The permissible stresses in service temperature of 50 ℃ and 80 ℃ are limited to be 470.0 MPa and 294.5 MPa, when service condition is chosen to assess 99.7% reliability prediction up to 10-7 h-1. In comparison to traditional safety factor method, Z′parameter method has achieved reasonable creep rate prediction with reliability of new high strength aluminum alloy by considering the scatter of creep rate data.