Formation of gold nanoparticles (GNPs) is a physicochemical process with two paralleling aspects, i.e., the redox process and the crystallization. Herein the classical JMAK model which was originally developed for phase transformation process was applied for formation kinetics of GNPs prepared through both chemical and biogenic approaches; the relationship between JMAK model parameters, the crystallization behaviors and the dimensionality of the GNPs were clarified. It reveals that the rate parameter k mainly depends on the nucleation rate, and the Avrami exponent n could reflect the nucleation mechanism and characterize the geometric dimension of GNPs. Also, the crystallization is the rate-determining process that controls the dynamic regime of GNPs formation. Mechanistic differences between the chemical and bio synthetic routes, as well as those between spherical and flaky GNPs are also clarified via interpretation of the JMAK model parameters.