Abstract: OTL(ocean tide loading) displacement inversion based on GNSS has a unique advantage given the rapid development of GNSS technology. It is more convenient, economic, accurate, and faster in comparison to gravity and VLBI (very long baseline interferometry) measurement on ocean tide loading. We conduct a systematic review on the progress of GNSS ocean loading research as this approach has drawn a lot of attention at home and abroad. We introduce the OTL displacement model for improving the accuracy of GNSS positioning, and obtain ocean tide loading information using GNSS. We point out the problems existing in the current OTL displacement models (the overall accuracy of the model is low, especially in the shallow water area) and the drawbacks of GNSS OTL displacement inversion methods (the emergence of pseudo anniversary, the existence of the system errors and the coupling effect between some tidal constituent and GNSS residual errors).