Abstract: The test method of consolidation by high confining pressure, freezing at low temperature and loading-unloading is employed to simulate the change process of stress state of underground engineering in Cretaceous frozen soft rock during construction. A large number of test results show that there is an initial critical stress threshold value in Cretaceous frozen soft rock, and it meets the Mises strength function criteria. The viscosity coefficient of frozen soft rock is a linear function of time, and the fitting correlation coefficient is up to 0.99. A frozen soft rock nonlinear viscoelastic-plastic creep constitutive mechanical model is proposed. The creep test results are compared with the calculated values, and their deformation laws are exactly the same and the values are in good agreement. The low temperature soft rock constitutive model is validated to be correct and can provide numerical calculation reference for the frozen underground engineering and geotechnical engineering in cold regions.