The influence of the surrounding rock creep of soft rock tunnel on the prestress of the anchor cable can not be ignored. In order to explore the relationship between rock mass and prestress loss under the creep coupling effect of prestressed anchor cable, this paper uses the theory of the component combination model and takes a soft rock highway tunnel in the west as the engineering background. The Nishihara model, with good applicability to describe the creep problem of soft rock, and the Hooke model describing the prestressed anchor cable are connected in parallel, and the Nishihara coupling model of anchor cable prestress changing with time under creep effect is established. The coupling model is used to calculate and analyze the initial stress between 15 ~ 30 MPa. The goodness of fit of the Xiyuan coupling model and the generalized Kelvin coupling model to the long-term monitoring value of the cable prestress. The results show that: The average goodness of fit of the Nishihara coupling model is 0.98, which is much higher than the average goodness of fit of 0.73 of the generalized Kelvin coupling model. It is proven that the calculation results of the Nishihara coupling model are better than the generalized Kelvin coupling model for the fitting of the monitoring data, and it is more suitable for simulating the prestress loss of the anchor cable under the long-term creep of the soft rock tunnel. The research results have certain guiding significance for the design and construction of prestressed support engineering.