The objective of the present work is to research the dynamic thermal performance of the solar power plant during the phase change material (PCM) capsule heat storage tank discharging process. Therefore, a transient, one-dimensional two-phase model for a packed bed latent heat storage unit and a comprehensive concentrating solar power generation system that combines a CO2 Brayton cycle and organic Rankine cycle were integrated. The influences of the key parameters of the packed bed PCM capsule heat storage tank on the overall power output and thermal efficiency of the system during discharge have been investigated, including the heat transfer fluid (HTF) velocity, the diameter of the PCM capsule, and the height of heat storage tank. The orthogonal analysis method is selected in this article, and the results showed that the maximal transient power output and overall power output of the actual combined cycle mode are decreased about 22% and 25%, respectively, in this research, compared with the idea Carnot cycle mode. That the HTF velocity in the thermal energy storage tank can be used to control the transient power output of the solar thermal power system. Using the small-sized filler capsule is an effective method to increase the thermal performance of the concentrated solar power (CSP) combined cycle system. Moreover, the corresponding discharging time is increased obviously, and the CSP with a high packed bed height can generate a more stable power output value during thermal energy discharging.