In the present research, uniaxial creep test was conducted under different axial compression levels at varying freezing temperature (-5℃,-10℃,-15℃) by WTD-100 artificial frozen soil apparatus to investigate the accelerating creep of frozen brown mudstone. The brown mudstone in a coal mine shaft in Shaanxi Province was taken as research object. Test results showed that the frozen brown mudstone experienced three stages of transient elasticity, deceleration and stability under low axial pressure, and four stages of instantaneous elasticity, deceleration, constant velocity, and acceleration under high axial compression level. The influence of axial compression on frozen brown mudstone is much greater than that of temperature. Moreover, by connecting nonlinear viscous dampers with strain start, an optimized Nishihara model with seven elements was established based on classical Nishihara model, and the model parameters are analyzed through nonlinear regression by the least square method. Analysis results showed that the fitting curves of the optimized Nishihara model are in good agreement with the experimental results. The optimized Nishihara model is more specifically suitable for describing the variation rule of nonlinear accelerating creep characteristics of frozen brown mudstone.