To address the engineering difficulty of inaccurate prediction of thermal holding time for large-size solid propellant charges，high and low temperature thermal holding tests and numerical simulations are carried out on a four-component HTPB propellant charge specimen.Temperature sensors are arranged inside the charge to collect time-series internal temperature data in real time，and the temperature variation rules throughout the whole thermal holding process are systematically revealed.A two-dimensional axisymmetric finite element model is established and validated by experimental data.The results show that the heat transfer process of the charge during thermal holding can be divided into three stages：temperature response stage，radial unsteady heat transfer stage and thermal equilibrium stage.In the radial unsteady heat transfer stage，the internal temperature of the charge follows a natural exponential law with time，while the shell surface temperature varies in accordance with the double natural exponential rule.In the thermal equilibrium stage，the temperature distribution presents a natural logarithmic function relationship with the radial relative position.Calculation verification indicates that the overall numerical error is less than 10%，with deviations of 5.5% and 9.9% under high-temperature and low-temperature working conditions respectively，which meets the engineering accuracy requirements.Revising the first-type boundary condition with the time-series fitting function of shell surface temperature can effectively compensate for errors caused by numerical model simplification and improve the calculation accuracy of heat transfer inside the propellant charge.