On the basis of establishing mechanics model, viscoplasticity theory and principle of minimum potential energy , temporal correlation of the filling body was analyze . The necessary conditions of the filling body’s stability and the formula of minimum steady time were obtained. Theory analysis shows that the filling body’s steady time decreases with the increase of plastic area; when elastic modulus, hardening parameter and coefficient of viscosity are exogenously decided. The filling body’s steady time decreases with the increase of elastic modulus, and increases with the coefficient of viscosity. Gradual failure theory indicates that plastic range of filling body has a close relationship with in-situ rock stress, it provides theoretical basis for parameter selection and design of the gob-side entry retaining.