In order to reveal the mechanism of nanofiltration during high salinity mine water treating. NaCl, MgCl, Na2SO4 and MgSO4 were selected as the typical chemical components of mine water. The effects of solution concentration and operating pressure on separation performance were studied through simulation test. The results show that the membrane flux of nanofiltration depended on the operating pressure difference between the both sides of membrane and the osmotic pressure difference of solute. The membrane flux was positively correlated with the operating pressure difference and negatively correlated with the osmotic pressure difference. When the mass concentration was 1 000 mg/L, the minimum membrane flux of chloride was 16.5 L/h and the maximum membrane flux of sulfate was 15 L/h. When the mass concentration was 2 500 mg/L, the minimum membrane flux of chloride was 13 L/h, and the maximum membrane flux of sulfate was 12 L/h. The rejection rate was affected by Donnan effect and screening effect,and the degree of influence depended on the ionic charge and ionic hydration radius, respectively. When the operating pressure was 0.1~0.4 MPa, the rejection rate of NaCl decreased from  38.9% to 19.5% the rejection rate of MgCl2 increased from 34.0% to 62.4%, and the rejection rate of sulfate fluctuated from 96.2% to 98.0% with the increase of the operating pressure and the concentration of the solution. The rejection rate of NaCl and MgCl2 increased first and then decreased with the increase of operating pressure which was in the range of 0.1~0.4 MPa. The maximum rejection rates were 33.9% and 51.5% when the operating pressure was 0.3 MPa. The minimum rejection rates was 27.6% and 41.9% when the operating pressure was 0.1 MPa. The rejection rate of sulfate fluctuated between 96.2% and 99.0%.