The invention relates to an omnidirectional circularly-polarized slot spiral antenna comprising coaxial joints, stepped transformation structures, an antenna radiator and a matching load. Each of thetwo ends of the antenna radiator is connected with one stepped transformation structure. Each stepped transformation structure is connected with one coaxial joint. One coaxial joint is connected withthe matching load, and the other coaxial joint is connected with the exciter of the antenna. Compared with the processing and mounting method of the existing omnidirectional circularly-polarized antenna, the omnidirectional circularly-polarized slot spiral antenna has the advantages of compact structure and simple processing, and can meet the corresponding electrical index and structural strengthrequirements.