Abstract: Anchor cable tension relaxation with time is a typical problem in the prestressed anchor cable structure used to reinforce slopes. In order to reasonably predict the tension relaxation of anchor cable, based on the interaction among the stable layer, anchor cable, slide mass and constraint components on the slope face in the anchor cable-slope system and the basic loading and deformation mechanism of the anchorage system, a four-body series rheological model composed of anchor cable, slide bed, slide body, and constraint components is established, in which the anchor cable and constraint components are simulated with Hooke body, the slide mass is simulated with Kelvin body or generalized Kelvin body, and the stable layer is simulated with generalized Kelvin body. The calculation equation of the anchor cable tension relaxation is accordingly derived. Some examples show that the error between the proposed value of cable tension relaxation and the observed results is smaller than those using the existing calculation methods. The maximum error of cable tension relaxation convergence value using the proposed method is about 11%, and the maximum error of the relaxation duration is about 10%. The relaxation rate of the anchor cable tension increases linearly with the diameter and elastic modulus of the anchor cable, and decreases nonlinearly with the increasing anchor hole spacing, the hysteresis elastic modulus and the viscosity coefficient (particularly in the initial stage) of the stable layer and slide mass. The instantaneous elastic modulus of the stable layer and the slide mass as well as the elastic modulus of the constraint components have little effect on the tension relaxation of the anchor cable. The proposed method can be used to quantitatively evaluate the anchor tension relaxation of slopes reinforced with prestressed anchor cables in practical engineering, which naturally allows to analyze the long-term stability of the anchored slopes.