This paper presents an energy flow uniformity measurement system and method based on CCD camera and dual Lambertian target. The system has two Lambertian targets, one of which is fixed and water-cooled. An heat flow detector at the center opening of the target is used to obtain the regional gray value. The other is a movable Lambertian target, which is used to capture spot images without a detector. The proposed method can directly obtain the pixel gray value of the detector area, making the measurement process simple and accurate. In this paper, the measurement principle and the entire process of extracting the energy flow density distribution of the gray images of the focus spot are described in detail. The platform is built and the spot energy flow distribution of multiple small heliostats is measured, verifying the correctness and feasibility of the proposed method. It can be seen from repeatable experiments and error analysis that the peak energy flow density error detected using the proposed method is less than 2.4%. The proposed method can be used for the energy flow distribution detection on the surface of the heat-absorbing tube at the opening plane of the secondary condenser in a linear Fresnel concentrator system.