Abstract The solar flux distribution rule inside a central cavity receiver is of great significance to the safe operation of solar tower power plants. In this paper, a heliostat field model was fully developed to simulate the solar flux distribution on the inner surfaces of a cavity receiver of a solar tower power plant by means of the Monte-Carlo ray-tracing method. In addition, the mathematical modeling process that starts from the incident solar rays to the absorbed energy by the inner surfaces of the cavity receiver was presented in detail. According to the final layout of the heliostat field, a dynamic simulation of the solar flux inside the cavity receiver during the vernal equinox was performed. The results indicated that the incident energy reflected by the heliostat field was mainly distributed on the rear and lateral surfaces throughout the day. Moreover, at different time points, the solar flux distribution rule inside the cavity receiver was also analyzed in detail. In order to verify the validity of this model, the simulation results were taken to compare with the experimental data of a random heliostat. Furthermore, to further testify the accuracy of our model, the simulation results obtained by inputting the coordinates of the CESA-I’s heliostat field into our model were also taken to compare with the published experiment data. Ultimately, both of the comparative results show that they can be good references for the safe design of the whole system.