To investigate the creep mechanical properties of tri-component hydroxyl-terminated polybutadiene （HTPB） composite solid propellant under different temperatures and stress levels， creep mechanical performance tests were conducted using a self-developed mechanical creep testing equipment， a temperature-humidity environmental chamber， and a high-definition camera. Tests were performed at environmental temperatures of 10 ℃， 25 ℃， 40 ℃ and 55 ℃， covering a stress range of 0.072 to 0.712 MPa . The strain-creep time curves were obtained， along with the variation patterns of typical mechanical property parameters with environmental temperature and stress level. A master curve for the creep rupture time， reflecting the propellant’s failure behavior under broad loading conditions， was established. The results indicate that， as the stress level increases， the characteristics of the propellant’s strain-creep time curve shift from three stages to four stages. Increasing environmental temperature reduces the critical stress level at which the four-stage curve characteristic exhibits， and this stress follows an exponential decay pattern， decreasing from 0.562 MPa at 10 ℃ to 0.262 MPa at 55 ℃ with a reduction ratio of 53.38%. The initial creep compliance increases with rising environmental temperature but remains almost unchanged with increasing stress level. When both environmental temperature and stress level increase， the creep rate increases， creep rupture time shortens， cumulative damage degree increases， and cumulative damage rate accelerates. In contrast， the fracture strain is primarily sensitive to changes in stress level and exhibits a linear increasing trend with increasing stress level. The creep rate under 55 ℃ and 0.412 MPa is approximately 493 times that under the same stress level at 10 ℃， and the creep rupture time is about 2.14% of that under the same stress level at 25 ℃. Finally， based on the double logarithmic test data of creep rupture time versus stress level under different environmental temperatures， and using the environmental temperature-stress level equivalence relationship， a master curve for propellant’s creep rupture time was established. At the same time， exponential mathematical expressions for this master curve and the temperature shift factor were obtained. Calculations using these expressions indicate that， to ensure a vertically stored SRM grain does not experience creep rupture failure within 15 years at 25 ℃， the loading stress level should be lower than 0.2176 MPa.