Using ocean reanalysis data, this paper studies the variation of sea surface salinity (SSS) in the North Pacific and its relationship with fresh water flux (FWF).Results show that SSS has an increasing trend from 1914 to 2013, with a periodic change of 25-30 a;From 1979 to 2013, SSS decreases first and then increases, with a periodic change of 7-12 a.The active areas of SSS variation in the North Pacific are located in the Kuroshio and its extension area (Area A) and the eastern central North Pacific (Area B).SSS in Area A and Area B shows a decreasing trend before 2000 and an obvious increasing trend from 2000 to 2009.Variations of SSS in Area A and Area B are significantly correlated with variation of FWF in the North Pacific.SSS in Area A is greatly affected by local FWF (The maximum correlation coefficient is 0.56 when FWF leads 16 months), and SSS in Area B is less affected by local FWF (The maximum correlation coefficient absolute value is 0.21 when FWF leads 20 months).Correlation between FWF in the North Pacific and SSS in Area A shows that there is a large range of positive correlation area, which is mainly located in the extension area of Kuroshio (east of Area A), and the high value area of positive correlation moves eastward with the shortening of FWF lead time.Corresponding to the interdecadal variation of temperature in the North Pacific, SSS also has significant interdecadal variation, and the variation of SSS in key areas of the North Pacific can characterize the North Pacific climate variability, which can be used as an alternative index of the North Pacific climate variability.