Energy flux density distribution of the concentrating collector can be used to evaluate the performance of the mirror field and the collector. The direct or indirect measurement methods commonly used to measure the energy flux density distribution often suffer from issues such as low accuracy and long measurement times. To address these problems, we propose an image processing based method for analyzing the solar-focused spot. It utilizes a megacam to capture images of the solar-focused spot, the irradiance values at different positions of the spot are calculated using a multilayer perceptron, and a novel energy flux density grading measurement method is proposed to improve the dynamic range of irradiance measurement. The mean absolute percentage error of the system is in the range of 2.5% to 3.5%, and the measurement period is about 2 s. The system does not require a diffuse reflection target and offers advantages such as high accuracy, fast measurement speed, short measurement time, and low sensitivity to environmental conditions. Experimental results validate the effectiveness and accuracy of the system in measuring the energy flux density of focused spots in different irradiance ranges, which provide a new idea for measuring the energy flux density of concentrating collectors.