He has been on Satellite Navigation, Space Geodesy, Remote Sensing and Space/Planetary Exploration. He established aresidual-based stochastic model with greatly improving GNSS accuracy; found a new method to estimate diurnal atmospheric tides by GNSS with overcoming the limitation of traditional techniques; established a high-precision ionospheric model with revealing the mechanism of ionospheric disturbances; proposed GNSS Remote Sensing direction with advancing the research and applications; revealed scattering mechanism with providing the foundation for GNSS-R applications; found strong correlations between GNSS atmospheric disturbances and seismic activities with revealing the mechanism of lithosphere-atmospheric coupling; and promoted planetary geodesy and remote sensing with obtaining new recognitions of the planet's surface and atmosphere. He has published over 500 papers in JGR, IEEE, EPSL, RSE, JG etc. and 10 books/monographs with over 9000 citations and H-index>50 as well as more than 10 patents/software copyrights and over 100 invited talks. He has led over 20 projects from Europe’s ESA, China-Germany (NSFC-DFG) and China’s National Key R&D Program and NSFC. He teaches Geodesy and Geophysics at the undergraduate and graduate level and has supervised over 30 Ph.D and 50 M.Sc as well as 20 Post-Docs.