Abstract: In order to realize real time water level control of large-scale sea area and meet the need of water level correction accuracy, we proposed a real-time water level calculation method of large-scale sea area by POM(princeton ocean model), blending assimilation method, least square fitting method and other methods. The precision tide model and water level correction model of multi-station were the basis of the real-time water level calculation method. The water level correction software of multi-station was developed and the long term, temporary tide station method and GNSS-PPK method were used to check the water level calculation results in Pearl River Estuary. The results showed that:① The accuracy of the tide model was 4.5 cm, which was higher than the accuracy international model.② The error range of the water level calculation results was within ± 5 cm and the medium error range of water level correction results of bathymetric data was within ± 15 cm, which could meet the needs of standard requirement. In the study area, the water level data in any place and time could be obtained with precision by the method. The method could provide real-time water level data for underwater topographic survey, dynamic guarantee of water level information in navigation, water regulation in dry season and saltwater intrusion study. This method can be applied to the Yangtze River Estuary, Hangzhou Bay and other sea areas.