Abstract: The theorem of corresponding relation between the neighbouring phase regions (expressed by N. P. Rs) and their phase boundaries and six corollaries of this theorem were derived from the principle of phase equilibria. According to them, there are definite relations between the dimension of phase boundary (set of equilibrium phase points) R₁,the total number of different phases in the two N. P. Rs Φ, the number of the common phases existing in the both N. P. Rs, △φ, and the dimension of common boundary (set of system points), R₁. Applying this theorem and its corollaries, the following results may be obtained. Both of the boundary rule and Palatnik-Landau's contact rule of phase regions in phase diagrams may be deduced. The ten empirical rules, concluded by F, N. Rhines and followed for constructing the complex ternary phase diagrams, may be put on a theoretical basis. The relations between the N. P. Rs and their boundaries in the phase diagrams of one-、two-、three-and four- components of different types may be explained without applying any supplementary conceptions.