The invention belongs to the technical field of the communication, specifically a Circular-polarized back-cavity waveguide slot array antenna realized near-field coupling polarizer. The antenna array is composed of two parts: the lower end is the linear-polarized back-cavity waveguide slot array with high gain and low section, and the upper end is a biparasitic corner-truncated patch polarizer; the corner-truncated patch polarizer is composed of two corner-truncated parasitic patches, each two patches are isolated by using a metal belt electrically connected with a metal through hole; the linear-polarized back-cavity waveguide slot array is composed of a coaxial interface, a feed waveguide network, a coupling slot, a resonant cavity, a radiation slot and a support column; a periodical metal prop integrally machined with lower end antenna is supported between the polarizer and the antenna array plane; the assembling is convenient, the structure is compact, the additional loss material is unnecessary to import, and the features of high gain and low loss of the original waveguide back-cavity antenna are maximally reserved; furthermore, the surface wave between a polarizer medium substrate and an air contact surface can be commonly inhibited, and the performance of the antenna is effectively improved.