Abstract: To study the seawater surface tension coefficient representation with different salinities and to simplify the test methods, a practical model for the bubble departure volume and the departure instantaneous velocity is built by analyzing the forces experienced by the bubble in the seawater. The underwater gas emission experimental platform is constructed. It uses the normal pressure air and six kinds of salinity seawater as the experiment's gaseous phase and liquid phase. And the bubble motions are categorized as slow motion with low Reynolds number and fast motion with high Reynolds number. Experiments with both bubble motions are conducted. The high-speed photography technology is used to record the bubble motion, and the filmed pictures are analyzed by the MATLAB program, so as to obtain the bubble departure volume and the departure instantaneous velocity. Substituting the experimental data into models, the seawater surface tension coefficient representation with different salinities can be acquired. The result shows that, under the non jet generation and flotation condition, the bubble is of small radius and has slow movement with low Reynolds number. The simulation results are in consistency with the measurement with high credibility and low divergence. The error is less than 2%.