The invention relates to a 4mm-focal length wide-angle high-light transmission day-and-night confocal lens. The optical system of the lens is provided with, in the order from front to back along the incidence direction of light ray, a front group A with negative focal power, a diaphragm C and a back group B with positive focal power; the front group A comprises, in order from front to back, a biconcave negative lens A-1 and a drum type positive lens A-2; the back group B comprises, in the order from front to back, a first gluing group of a biconvex positive lens B-1 and a biconcave negative lens B-2, a positive meniscus lens B-3 and a biconvex positive lens B-4. The 4mm-focal length wide-angle high-light transmission day-and-night confocal lens has the advantages of wide angle of field of view, high light transmission, high resolution, simplified optical structure and low material prices, and can used both at daytime and night, and can be matched with a 3 million-pixel high-resolution CCD or CMOS.