To describe the complex behavior of overconsolidated soil，an improved overconsolidation state variable subloading surface model was presented. The multiple impact of plastic volumetric and shear strain on overconsolidation state variable R was considered in hardening equation. The stress-update algorithm and the procedure of numerical implementation were introduced. The the model was applied by compiling the interface subroutine in finite element software ABAQUS. The rationality of the subroutine was verified by numerical simulations in different working conditions and load types. At last，Fujinomori Clay was simulated by the model in compression test，and the results were compared with those of UH model and experimentation data. The subroutine was precise and steady andthe model proposed can describe the properties of overconsolidation accurately.