Portland cement paste specimens made with different water cement ratios of 0.35,0.45 and 0.55 were partially immersed in 5% Na2SO4 solution under a constant nitrogen atmosphere and at temperature of(20±1)℃ and(80±5)% relative humidity. After 50, 100d partial immersion, the chemical attack products in the evaporation zone and immersed zone of specimens were quantitatively analyzed by means of X ray diffraction and thermogravimetry. Test results show that the content of chemical attack products of ettringite and gypsum formed in the evaporation zone is much more than that in the immersed zone, and the content difference of products between the two zones grows with the increase of partial immersion time. After 100d partial immersion, the content difference of products between the two zones in the paste with water cement ratio of 0.55 is double than that of the other two pastes. The test results quantitatively confirm that the damage of evaporation zone of concrete partially immersed in sulfate environment is mainly caused by the chemical sulfate attack.