The critical temperature of thermal explosion (T_cr) of PBX-A explosive chargers containing (AP) with diameter of 10, 15, 20, 30 mm and 40 mm and ratio of length to diameter of 1:1 was measured by self-developed test device of determining the critical temperature of thermal explosion of explosives and propellants. The critical temperature of thermal explosion and 5 s explosion temperature of PBX-A before and after aging 70 days under 85 ℃ was measured by the T_c measurement and an explosion temperature test apparatus. The degree of responses to the constant temperature heat stimulus, critical temperature of thermal explosion of charge with different diameter, relationship between time to ignition (t) and temperature (T) and change of thermal performance of PBX-A explosive before and after aging was obtained. Results show that the combustion of unconstrained PBX-A explosive charger with diameter of less than 40 mm only occurs at a constant temperature. The value of T_cr extrapolated by the fitting equation is over 120 ℃ for PBX-A explosive charger with diameter of 1 m and ratio of length to diameter ratio of 1:1. The linear relationship between lnt and 1/T can be true only in a very narrow temperature range. The T_cr of PBX-A explosive charger after aging 70 days under 85 ℃ does not change, however, its 5s explosion temperature decreases by 4.6 ℃.