Nowadays, global climate change is resulting in sea level variations due to global warming and glacier melting, which affect human living environments, especially ocean coasts. there exists some methods for monitoring the variations in tidal level, such as tide gauge station, satellite altimetry, Global Navigation Satellite System Interferometric reflection (GNSS-IR) and so on. With the steady progress of global navigation satellite systems such as BeiDou Navigation Satellite System (BDS) and Galileo, coupled with the increasing number of continuously operating reference stations (CORS) around the world, multi-GNSS monitoring of tidal levels has become possible in real time. Monitoring tidal variations by the onshore multi-GNSS in this article, MAYG is one of the Multi-GNSS Experiment (MGEX) stations in Mayotte, France. The GPS(L1,L2,L2c,L5), BDS(B1,B2,B3), and Galileo(E1,E5a,E5b,E6) observations are been used from January 1 to January 3, 2016. The co-located tide gauge station is Dzaoudzi with about several meters far from the MAYG station, with sampling rate of 1 min are provided by the Intergovernmental Oceanographic Commission (IOC). Signal-to- Noise Ratio (SNR) data is used from the multi-GNSS station MAYG based GNSS-IR to retrieve the tidal variation, which are compared to tide gauge observations. In this paper, We choose the effective elevation angle is 5-18 degrees, meanwhile, the varying reflector height is considered to be less than 7 m. Results show that the tidal variation from GNSS-IR have a good agreement with tide gauge, correlation coefficients of 0.68–0.92 and RMSEs of less than 0.42m, the best result of GPS-IR which was used L2c band, Similarly, BDS-IR is B3 and Galileo-IR is E1. The result of GPS is somewhat better than the other two systems, the result of Galileo is better than BDS. Therefore, we choose L2C, B3 and E1 to jointly invert the tidal variation, correlation coefficients of 0.88, MAE of about 0.15m and RMSE of about 0.18m. The research verifies the feasibility and effectiveness of multi-GNSS-IR in monitoring the tidal variations. It has enriched the data sources and increased time resolution used by 1multi-GNSS for inversion of ocean tides, which has expanded the application of GNSS remote sensing in the ocean.