In order to meet the increasing bandwidth requirements of wireless communication, expand the impedance bandwidth and axial ratio bandwidth of circularly polarized microstrip antenna while maintaining the miniaturization of wireless equipment, this paper proposes a design of broadband circularly polarized microstrip antenna based on microstrip slot antenna. The overall size of the antenna is 30 mm×30 mm×1.6 mm, the top structure is an inverted S-shaped branch, and the eccentric side feeding mode is adopted. The impedance matching of the antenna is improved by loading a stub on the microstrip line, which expands the impedance bandwidth of the antenna, and the axial ratio bandwidth of the antenna is expanded by chamfering and trenching the ground plate. The measured results show that the -10 dB impedance bandwidth of the antenna is 62.1% (5.16~9.81 GHz), and the 3 dB axis specific bandwidth is 63.9% (4.43~8.59 GHz). The antenna has the characteristics of small size and wide band, which is suitable for the wireless communication system in the 5.8 GHz band and WiFi-6E band.