The Rayleigh-Taylor instability is numerically studied through the Large-Eddy-Simulation (LES) approach.The whole evolution process of the instability is achieved,including the linear stage,the regular nonlinear stage,the irregular nonlinear stage and the turbulent mixing stage.The characteristic of the interfacial motion and the growth of the mixing layer thickness are analyzed.And the averaged turbulent energy as well as the flux of passive scalar is calculated at both the resolved scale and the subgrid scale.The LES method is proved to be an effective approach for the simulation of the Rayleigh-Taylor instability.