Based on interpreting the importance of statistical work of soil parameters

uncertainties

the theoretical foundations and superiorities of many statistical methods are analyzed and contrasted. The research results about soil variability are summarized systematically via reviews and collections of the involved literatures at home and abroad

including index parameters

deformation parameters

strength parameters

consolidation parameters of lab tests and the parameters from CPT

VST and SPT. It is shown that the traditional method and the three-sigma rule

which are both based on the random-variable theory

will never overcome defects of model itself in spite of improvements in any case. The random field-based approaches model the soil profiles by superior random field theory and show strong vitality. It will replace the traditional method along with gradually mature of in situ tests finally. The graphical three-sigma rule

converging theoretical advance and applicability

is a worthy recommended method. The results of soil variability show that the variations of laboratory index parameters are small

the laboratory consolidation parameters are big and the other parameters from lab tests and in situ tests are in the middle. The results also show significance for selecting and optimizing parameters and reliability analysis of some important projects.