It is important to calculate solar flux distribution with a precise and simple method for the design and optimization of solar tower systems. In this paper, the Gaussian flux density function at the image plane is deduced after simulating the image function of the heliostat with Gaussian distribution function. The flux density distribution of various round or rectangular focusing heliostats at the receiver plane can be calculated through projection. The simulation results are compared with SolTrace analysis and experimental data. Comparison of the flux density distributions between this method and SolTrace show excellent agreement especially when the optical error is equivalent to or larger than the Gaussian function parameter of heliostat image which fits to most of heliostats in a solar tower system. Although it increases error to simulate the image of the heliostat with elliptical Gaussian distribution, compared with the experimental data, the average prediction error of the elliptical Gaussian function is 2.24%, which is less than that of SolTrace because SolTrace applies the circular Gaussian distribution for optical error which bring more errors. Therefore, the Gaussian flux density function proposed is validated and can be used to simulate and optimize the design of solar heliostats field. (C) 2018 Elsevier Ltd. All rights reserved.