Considering the viscous coefficient as an indefinite constant, a nonlinear functional relationship of viscous coefficient is established, and a nonlinear rheological mechanical model for describing the whole process of rock creep is proposed. Under a certain condition, the model can be transformed into Burgers or Nishihara Masao model. Under the condition of constant stress and constant strain, the creep and rheological equations are deduced, and the rock nonlinear creep and relaxation properties are studied. The creep test results of rock under different stress conditions are fitted, and compared the proposed nonlinear rock rheological mechanical model with the rest result, indicates that the test curve tallies with the theoretical curve, and proves the correctness and rationality of the proposed model.