The stability of the live and reheat steam temperatures is of great significance for the efficient, flexible and safe operation of coal-fired power plants. The double reheat boilers are large inertia, non-linearity and high coupling. Therefore, the temperature controls of live and reheat steams are very difficult during load cycling processes. The heat storage in the double reheat boiler changes during load cycling process, which will affect the performances of temperature control. In this study, dynamic simulation models of an ultra-supercritical double reheat tower boiler and its temperature control models are developed based on the GSE software. These models are validated. Then, changes of the boiler system heat storage during different load cycling processes are studied. Results reveal that the metal heat storage is more than working medium ones at steady state load. However, the changing quantities of working medium heat storage are more than the metal ones between different loads. During load cycling processes, the changing tendencies of reheat steam temperatures, the difference of heat storage between real-time and steady state values (DHSBRS) and the difference of coal feeding rate between real-time and steady values (DCBRS) are similar. The fluctuations of reheat steam temperatures have a delay compared with DHSBRS ones, and the fluctuations of DHSBRS fluctuation have a delay compared with DCBRS ones. The delay time increases with the load cycling rates. The results are aimed at providing some guidance for the control system design of the double-reheat boiler system and the safe and flexible operation of power plants.