Aiming at defects of the poor uniformity of spotlight distribution and the mismatching between the focusing spot shape and solar cells for the traditional point focusing Fresnel lens, a Fresnel lens is proposed to uniformly focus square spot by sub-region multi-focus superposition. Four angle-missing isosceles right triangles were intercepted from the traditional circular concentric rings spot focusing Fresnel lens and spliced seamlessly to form a Fresnel lens uniformly focusing square spot by sub-region four-focus superposition, and the concentration uniformity is improved effectively by light superposition in the four parts. The ray tracing method was used to simulate and analyze the influence on the optical performance parameters such as the shape of the focal spot, the concentration uniformity and the irradiance, which is caused by the structure parameters of lens such as ring spacing, angle-missing chord length and waist length. The results show that the focus spot shape of the lens designed by this method is square, and the concentration uniformity is higher than 90%.