Abstract: A high-efficiency and multi-functional metasurface polarization converter that consists of a periodic array of double-split-ring resonators on an F4B-2 dielectric substrate is proposed. Through the interaction of double-split-ring resonators, the working bandwidth of the converter is effectively improved. The finite integral method is used to analyze the polarization characteristics. The simulation results show it can realize linear-to-circular polarization conversion over the frequency band from 5. 5 GHz to 8. 55 GHz (relative bandwidth of 43. 4%), and its energy conversion efficiency is better than 99. 5%. Moreover, linear-to-cross polarization conversion is also achieved in another frequency band from 10. 31 GHz to 15. 31 GHz (relative bandwidth is 39%), and its polarization conversion ratio is greater than 0. 99. In the experiment, a sample is prepared and its polarization conversion characteristics are tested. The experimental results are in accordance with the simulation results, verifying the rationality and effectiveness of the converter design. The proposed metasurface has the characteristics of high efficiency, large working bandwidth, multifunctional capability, and can be applied to wireless communication and polarization manipulating devices.