In this paper, a multi-mode substrate integrated waveguide (SIW) broadband circularly polarized antenna array based on metasurface is designed. Firstly, a half-mode SIW and a quarter-mode SIW are formed by etching slots on the top surface of the circular SIW resonant cavity antenna respectively. While miniaturizing the antenna using the multi-mode feature, the antenna bandwidth is expanded by 5.1%. Secondly, the introduction of metasurface further enhances the overall performance of the antenna sub-array and the bandwidth is increased by 1.8% while the gain is 1 dBi. A 2 Â 2 array is designed to verify the accuracy of the design, and a sequential rotating feed network was used to enhance the circular polarization characteristics. The final antenna size is 1.04 Â 1.04 Â 0.08λ 0 , which achieves 15.4% (4.46-5.2 GHz) operating bandwidth, 9.1% (4.55-4.98 GHz) axial ratio bandwidth, and maximum gain of 11.42 dBi in the operating band. The simulated results and measured results agree well which show the validity of the design.