We described the relationship between soil solution concentration and electrical conductivity with the fuction of three spline in Tarim irrigation district..The result showed that C = 0.0003EC3 - 0.0099EC2 1.6988EC - 0.9881.We caculated out that the solubility of the soil solution salt in Tarim irrigation district was 8.99 under the condition of 11℃，100mL soil solution with the same soil and piecewise function. We also caculated out that the quality of dry soil should between 5.72g and 24g. The result showed that purified water could instead of aqua destillata in determining soil solution salt in Tarim irrigation district.The error of determination was less than 0.03 with purified water .The error which caused by purified water was no more than 0.005.The content of volume moisture is beter no less than 0.2cm3/cm3 to accurately determine the content of the soil solution salt in Tarim irrigation dictrict.This method was simple and obviously improved the efficiency of the experiment.The result of the determination was accurate.