Abstract: The two-temperature or multi-temperature approach used in the study of nonequlibrium flow cannot describe the distribution at vibrational energy levels and assumes Boltzmann distribution under vibrational temperature instead. Detail study of the characteristics of nonequilibrium process with state-to-state model may inspire the improvement of the two-temperature or multi-temperature approach. In this paper, the state-to-state model is used to simulate the thermo-chemical nonequilibrium process of a stationary closed N2/N mixture system. The time evolution of the density of N and N2 at different levels and the relaxation of vibrational distribution under different controlling conditions (temperature, pressure or density) and different initial conditions are analyzed, the characteristics and contribution of each micro processes are investigated. The results show that: (1) The vibrational translational energy exchange processes are the important processes which drive the vibrational distribution to Boltzmann distribution, while the vibrational vibrational energy exchange processes only affect the characteristic of the transition course. (2) The departure of population distribution from Boltzmann distribution prevails in thermo-chemical nonequilibrium flow, and the evolution of the vibrational distribution for dissociation regime and that for recombination regime are different. (3) The results obtained from the study of thermo-chemical process with state-to-state model would help to thorough comprehension of the nonequilibrium phenomenon, and may provide reference for the improvement of thermo-chemical model used in the simulation of hypersonic nonequilbrium flow.