The invention relates to a nested dual-arm planar helical antenna for achieving multi-OAM mode generation. The antenna structure is divided into three layers, a first layer is a microstrip spiral structure, a second layer is a metal reflector, a third layer is a feeding network portion of the antenna, and an output port of a feeding network passes through the metal reflector to connect the microstrip spiral of the first layer. The microstrip spiral structure comprises a top dielectric plate, three dual-arm spiral lines printed on a top of the top dielectric plate, and a metal disc and a metalring printed on the bottom of the top dielectric plate. The feeding network comprises a metal ground at the top and three one-to-two power splitters at the bottom. Output ports of the three power splitter respectively correspond to the three dual-arm spiral lines. The dual-arm spiral lines at the top of the first layer are connected to the power splitters at the bottom of the third layer through inner conductors of the coaxial lines, and the metal disc at the bottom of the first layer passes through the metal reflector through a coaxial outer conductor to connect the metal ground at the top ofthe third layer.