Abstract: The underwater glider can record the data of temperature, salinity and pressure of sea water efficiently.However, due to the thermal lag effect, the salinity data, especially in the thermocline with large temperature gradient, should have produced a certain degree of deviation. In this study, three commonly used salinity thermal lag correction methods were selected to correct the deviation caused by thermal lag effect of salinity data observed by sea-wing underwater glider with pump in the central North Pacific Ocean in August 2019. The results are compared with the salinities recorded by shipborne 911 conductivity, temperature and depth measuring instruments (CTD). The reduction degrees of deviation of upcast and downcast profiles before and after the application of three methods for salinity correction of glider are compared. The optimal method of salinity correction for the underwater glider is obtained. That is, on the premise of correcting the actual temperature in the conductivity cell, the computer graphic segmentation method is used to minimize the objective function determined by the area surrounded by T-S curves of the downcast and upcast profiles. Finally, the thermal lag correction amplitude and time constant could be determined to correct the salinity deviation between the downcast and upcast profiles.