A total of 32 daily PM2.5 samples were collected from December 2016 to February 2017 in the urban area of Xuzhou city. Water-soluble inorganic ions (WSⅡs), including F-, Cl-, NO3-, SO42-, Na+, Mg2+, NH4+, K+ and Ca2+, were determined by ion chromatography. The average mass concentration of PM2.5 was (164.8±77.3) μg·m-3 and the average total mass concentration of the nine ions was (67.5±36.1) μg·m-3, the contribution of the WSⅡs to the PM2.5 was more than 40.9%. The order of the concentrations of individual ions was NO3- > SO42- > NH4+ > Cl- > Ca2+ > K+ > Na+ > Mg2+ > F-. NH4+, NO3-, and SO42- (SNA) were the major components of the water-soluble ions in the PM2.5 measurement. The average mass concentration of WSⅡs in clean air, mild haze, and severe haze was (12.8±8.8), (59.0±22.8) and (86.3±36.0) μg·m-3, respectively. The contribution of SNA to WSⅡs was 86.4%, 82.8%, and 78.9%, respectively. The correlation between each component of SNA with each other was significant. NH4+, NO3-, and SO42- were in the form of (NH4)2SO4 and NH4NO3. Secondary formation, biomass burning, fossil fuel combustion, and dust were the major sources of the water-soluble ions in PM2.5.