A new thirdorder relaxation scheme for hyperbolic conservation laws was presented, which combined thirdorder WENO reconstruction for spatial discretization with thirdorder implicitexplicit RungeKutta method for time discretization. The new scheme is much simpler and less computationally expensive than the original one. The resulting scheme does not require Riemann solvers and the computation of Jacobians, so it remains the advantages of relaxation schemes. The new scheme was tested on several numerical examples, and the results showed it had high resolution.