A novel circular porlarization (CP) antenna is designed and fabricated by loading a kind of polarization conversion metasurface. The structure of polarization conversion metasurface is composed of metal slash and copper ground sheet, which is separated by an FR4 dielectric substrates with a thickness h=3 mm. When a normal electromagnetic wave incident on the whole surface vertically, the electric field of the wave can be decomposed into two components Evi and Evi. Under the excitation of the two components, resonance is induced between the metal slash and the copper ground sheet respectively, making their own reflection phase changed to = u - v = 180, eventually making the reflection wave appear with 90 polarization rotation. By taking the peculiarity of 90polarization rotation of the polarization conversion metasurface, we can modulate the linear polarization of microstrip slot antenna into the circular polarization radiation. Through adjusting the distance between the slot antenna and the polarization rotation metasurface, we can regulate the working frequency of the circular polarization. Simulated and experimental results show that the polarization conversion metasurface makes a high-efficiency polarization rotation at 8-12 GHz. And the center working frequency of the CP antenna is 9.1 GHz, the impedance bandwidth is 8.3-10 GHz. When the distance H = 4.5 mm between the microstrip slot antenna and the polarization conversion metasurface, the 3 dB axial ratio bandwidth is 8.3-8.8 GHz, the microstrip slot antenna may realize circular polarized radiation. When H = 20 mm, the 3 dB axial ratio bandwidth is 8.8-9.3 GHz, and the slot antenna can realize circular polarized radiation. When H = 8 mm, the 3 dB axial ratio bandwidth is 9.3-10 GHz, the slot antenna can realize circular polarized radiation. Experimental results are in agreement with the simulation results, showing the validity of this design method which may become a new approach for the CP antennain designing