Different sampling sizes and spatial interpolation methods will affect the accuracy of prediction of soil properties. This study selected Mengcheng County in Northern Plain of Anhui Province as an example. 50 samples were selected from total 550 soil samples as validation subset using random sampling method. The five samples subsets, 500, 400, 300, 200, 100 samples, were extraction from remaining 500 samples. Ordinary kriging, inverse distance weighting method, local polynomial, radial basis function interpolation were used to research spatial variability of soil organic matter, and independent validation and cross-validation were used to compare the accuracy of predictions of different sampling sizes and spatial interpolations. The results showed that: different number of samples will have a greater effect on the regional soil properties prediction accuracy in northern Anhui plains county scale, digital soil mapping property for the purpose of soil sampling, approximately 200 samples is reasonable sampling number. Different interpolation methods on prediction accuracy was not significant from a cross-validation and independent verification of the root mean square error, the ordinary Kriging optimal, local polynomial interpolation and radial basis function method followed by inverse distance weighting interpolation results most difference.