Abstract: Aimed at the problem of the salt bed wellbore creep and shrink under the drilling,based on the elasto-plastic mechanics theory and the head creep equation,the new formula of the control wellbore shrink rate was derived with in case of the plane strain and uniform in-situ stress,which was different from the old formula.By the theoretical analysis,the difference of the formula is the creep stress difference,the verification of the formula used the finite element method(FEM) was presented,it proved that the result of the theory formula is in agreement with the FEM,the result of the old formula was big error with that of the FEM.It proved that the new formula of the drilling mud density is correct.