Abstract: The red bed soft rocks in central Yunnan are widely distributed and have significant rheological properties. In order to study the creep properties of red bed mudstones under saturated-dehydration cycle conditions,Longchuan River valley mudstones are used as research objects. YZJL-300 rock shear rheometer performs 30,50,and 100 shear creep tests on saturated-dehydration cycles. A constitutive model of mudstone creep is proposed by analyzing the shear creep characteristics of mudstone. The test results show that:(1)the limit instantaneous creep rate gradually increases 0.273 mm·h^-1,0.365 mm·h^-1,and 0.452 mm·h^-1 as the number of saturated-dehydrated cycles increases and the long-term strength gradually decreases; (2)under the same shear load,the greater the number of cycles,the lower the viscoelastic modulus of mudstone; the same number of cycles,the larger the shear load,the smaller the viscoelastic modulus of mudstone. The function of the number of cycles and time is E(n,t). A non-linear viscoplastic body is introduced to establish the shear creep constitutive model(LCJN) of the inverted siphon mudstone of the Longchuan River and a general global optimization method to identify parameters of LCJN model,and verify the accuracy and applicability of the model.