Abstract: This paper introduces the design of a W-band broadband multi-mode vortex electromagnetic wave Cassegrain antenna. A circular waveguide array is constructed with a dual-polarized open square waveguide as an element. Combined with a multi-mode feed waveguide network, the vortex wave mode ( \mathitl=0,\pm 1,+2 ) is independently multiplexed with the polarization (X-polarization, Y-polarization), and used as the feed of the Cassegrain reflector antenna, realizing consideration design of multi-mode, wide bandwidth, high-gain beam. The simulation results show that the Cassegrain antenna can provide beams of 8 modes, the -10dB impendence bandwidth exceeds 24.4%, covering a frequency range of 72-92 GHz, and the gain of each mode exceeds 46.1 dBi. The design can be used for vortex electromagnetic wave transmission in the distance of hundreds of meters, which provides a new solution for the terminal design of high-speed multiplexing transmission system.