In order to reveal the creep characteristics of red bed mudstone with wide distribution in Southwestern China under different water content conditions, the rock triaxial creep testing machine YSJ-01-00 is used to carry out the triaxial compressive creep test. Experiment results show that: (1) On the whole, with increasing of water content and the lifting of the axial load, the ratio of creep strain and instantaneous strain is increasing. Also, the ratio range is 0.117-0.985, and the average ratio is maintained at 0.348-0.480. (2) The initial, steady and ultimate accelerated creep rate increase with the rise of water content. (3) The long-term strength of red bed mudstone decreases with the rise of water content. By quantitative comparison, it is found that the nonlinear creep degree of red bed mudstone is more obvious with the increase of water content. Therefore, in the construction of important project, the influence of water content on the creep characteristics of red bed mudstone should not be neglected. Based on the nonlinear characteristics of red bed mudstone, a viscoelastic modulus is proposed; and a new improved Burgers model is established by introducing a nonlinear viscoplastic body. Based on the BFGS algorithm and the general global optimization method, the creep test curves are identified; the model parameters are determined; and the reliability of model is analyzed; and the correctness and rationality of the model are verified.