The knowledge of heat flux distribution on the receiver area is very important to improve the overall performance of the solar Concentrating Photovoltaic (CPV) system. In a CPV system, non-uniform flux distribution is one of the common issues. Non-uniform illumination of heat flux is mainly due to the limitations in the design of concentrator optics, slope error in the concentrator profile, tracking system error, misalignment of concentrator, and the efficiency of refractive lens/reflecting mirrors. The prediction of the heat flux distribution will play a vital role in the CPV system such as designing the receiver area, selection of the materials, thermal management and to estimate the power output. In this paper, an experimental work for in-situ prediction of heat flux distribution profile on a flat plate receiver is presented. Inverse heat transfer technique is adopted to predict the heat flux distribution. A Gaussian distribution is assumed to model the distribution of the heat flux. The forward problem is a 3-D steady state heat conduction equation subjected to convection and radiation heat loss boundary conditions. The forward problem is solved using Finite Element Method in Ansys APDL. The unknown parameters of the assumed heat flux distribution are then estimated by minimizing the sum of squared error between measured and simulated temperature distribution. A deterministic search technique, Levenberg-Marquardt algorithm is used to solve the inverse problem. The simulated temperature distribution with the predicted heat flux are in good agreement with the measured temperature with a maximum residue of +/- 5 degrees C. Also, the deviation between theoretical and predicted total solar energy is found to be < 6%.