In order to understand the space-borne GNSS Reflection (GNSS-R) performance, an end to end simulator named GREEPS (GNSS-R End-to-End Performance Simulator) was developed by National Space Science Center (NSSC), Chinese Academy of Sciences. The simulator consists of four functional modules: Mission analysis module, forward modeling module, observation system modeling module and inversion/retrieval and precision Analysis module. This paper introduces each module's structure and capabilities. The preliminary simulation results are shown, including average and maximum number of simultaneously reflected GNSS satellites for 24 hours, coverage ratio between the ± inclination of LEO for 24 hours, the sensitivity of Delay Doppler Map (DDM) to the wind field, and wind field and ocean altimetry retrieval precision analysis. GREEPS is a powerful and useful simulation software for space-borne GNSS-R mission and payload design, it will speed up the space-borne GNSS-R applications in China.