The invention discloses an anchor wire prestress loss and rock-soil body creep coupling based computing method for side slope creep values. The computing method comprises the following steps: selecting the side slope that is comparatively uniform in soil body materials and properties and low in stability; determining the physical and mechanics parameters of the rock-soil body of the side slope; determining the water content W, the volume weight r, the uniaxial compressive strength Rc, the tensile strength Rt, the deformation modulus Eo, the cohesive force C and the internal frictional angle Phi of the rock-soil body; determining the creep curvilinear equation of the rock-soil body; determining the instantaneous elastic modulus Eh, the lagging elastic modulus Ek and the viscosity coefficient Eta of the rock-soil body; bringing all the parameters into the relaxation equation of the coupling effect computation module, and working out the relational expression of the variation of anchor wire stresses and time; computing the anchor wire stress value at each time point according to the relational expression of the variation of anchor wire stresses and time, and figuring out the anchor wire prestress loss according to the anchor wire stress calculated value at each time point. The computing method can correctly reflect the variation situation of the strained condition of the prestressed anchor wire.