Abstract: This paper deals with the investigation of the data of variation of sea level continuously recorded during many years by 5 tidal stations located along the coast of the Gulf of Bohai. After processing the data and making various corrections, it was found that before the Haicheng Earthquake of 1975 the average sea level showed a tendency of steady rise within a broad area. For the recording stations closer to the epicenter of the earthquake, the variation of the sea level became more conspicuous and abrupt. However, before the Bohai Earthquake, occurred in the Gulf of Bohai in 1969, the mean sea level was lowered for a long period of time.