<p>The mechanical and engineering properties of soil have regional characteristics, but determining how to characterize the regional soil properties with specific parameters and functions has always been an unresolved essential problem. This paper establishes for the first time the concepts, principles, and necessary foundations related to the theory of regional soil properties. Definition of regional soil is presented and drawing on the classical soil mechanics theory, the concept of dual control parameters (DCP) is proposed. Based on DCP, the concept and the construction criteria of regional soil characteristic functions (RSCF) are established. The idea of using the <i>N</i>-<i>V</i>_s (SPT-<i>N</i> and shear wave velocity <i>V</i>_s) relationship in a region as a kind of the RSCF is proposed. The principle of the <i>N</i>-<i>V</i>_s characteristic function (NVCF) is expounded, and the scientific nature of the NVCF is verified by using global in-situ data. The number of <i>N</i>-<i>V</i>_s elements required to construct the NVCF and the simplified evaluation method for the difference of the NVCFs are presented.</p>