Based on the analysis of mathematic model of ring laser gyro (RLG) and the principle ofcubic spline data interpolation,pointing to the data of practical input-output characteristic curve of someRussian model of RLG and making analysis and treatment with the cubic spline data interpolationmethod,the mathematic model applying to error compensation in the nonlinear working range and beingaccordance with the practical gyro characteristic has been deduced. The method proposed in this papercan be applied to accuracy compensation of the RLG with worse linearity and lower working accuracy inthe working range.