The spatial variability of soil salinity was studied using the methods Ordinary Kriging (OK) and Radial Basis Function (RBF) in Alxa Zuoqi of Inner Mongolia, and the optimal method of assessment on the spatial variability of soil salinity was determined by comparing OK and RBF on the spatial distribution trend of soil salinity and interpolation accuracy. The results showed that soil salinity had a strong spatial autocorrelation in Alxa Zuoqi. Soil salinity of high levels was mainly distributed in the south-west and north areas of Alxa Zuoqi, while the low level was mainly in the southeast and central areas. Profile distribution of soil salinity showed obvious regional characteristics, the salinity in bottom soil was the greatest in north area and the salinity in surface soil was the greatest in southwest and eastern areas. OK method had better interpolation accuracy and spatial distribution than RBF method. The 97.72% and 99.89% of areas suffered from different degrees of salinization in 0–20 cm and 20–40 cm layers. The proportion of moderately salinity was the largest in the study area, followed by heavy salinity and slightly salinity. There was a certain proportion of solonchak soil in Alxa Zuoqi. The above results indicate that the effective measures should be taken to prevent and control soil salinization in in Alxa Zuoqi.