Conventional methods for evaluating aging effects of solid propellants stored at natural temperature need long-term (at least 10 years) and detailed (at least daily) environment temperature data. It is very difficult or expensive to access those data in storage places. Even if the data has been obtained, it would be a very heavy workload to process them. A novel method has been established to substitute the conventional methods limited by data acquisition and processing. The method is based on monthly average temperature data. According to seasonal and diurnal variation models of natural temperature, the parameters of these models have been calculated from monthly average temperature data and local climate characteristics. Therefore, the aging equivalent temperature could be evaluated, and the natural temperature aging effects could be predicated. This method is simpler than conventional method in data processing. And the required temperature data of the method can be easily obtained through public ways. Aging equivalent temperatures of three typical solid propellants （(hydroxyl-terminated polybutadiene(HTPB）, nitrate ester plasticized polyether (NEPE）, composite modified double-base（CMDB)） stored in four typical regions was calculated by the novel method. Results show that the aging equivalent temperature is much higher than the annual average temperature. The difference between the aging equivalent temperature and the annual average temperature increases with the increase of the annual temperature range. As the aging activation energy of solid propellant increases, the aging equivalent temperature approaches the maximum monthly average temperature, and the difference between the equivalent temperature and the annual average temperature becomes larger.