In order to evaluate the class of exposure to sulfate attack of soil, different methods were intended to measure the sulfate concentration of soil in contact with concrete in different countries. Different methods of soil extracts preparation were used to determine the sulfate ion content of soil in this paper. Two artificial soils and one natural soil were prepared in these tests. The experimental parameters investigated in the study were: acid or water extract, water to soil ratio and agitating time. When samples were prepared by water-extracting method, water to soil ratio (2:1, 5:1 and 10:1) and agitating time (3min, 6h, 16h and 24h) were considered. The results show that the difference of sulfate concentration determination results using different methods was significant. The determination results of dilute hydrochloric acid extracting solution are higher than that of water extracting solution of the same soil sample. The sulfate concentration determination results of the same soil sample have increased with the increase of water to soil ratio or agitating time. The water to soil (W/S) ratio is more sensitive than agitating time to the sulfate concentration determination results.