In order to meet the needs of high bandwidth and circularly polarized communication in future wireless communication, a circularly polarized terahertz antenna based on a Fabry-Perot cavity is proposed. The antenna adopts a quasi-optical waveguide feeding mode, the circular waveguide is cut at 45° to realize the linear-circular polarization conversion of the antenna, and the partial reflecting surface of the dielectric material is used to improve the gain of the antenna. The simulation analysis shows that the maximum gain of the antenna is 14.4dBic at 228GHz, the impedance bandwidth (S11<-10dB) is 40GHz, the 3dB gain bandwidth and the axial ratio bandwidth are 18GHz and 27GHz respectively, and the overlapping bandwidth of the three is 18GHz. The antenna has the advantages of good directivity, high bandwidth and circular polarization in the entire working frequency band, and has high reference and practicability in terahertz/millimeter wave wireless communication.