Abstract: Effectively representing model uncertainty is crucial for improving the forecast skill of convection-permitting ensemble prediction system. The stochastic perturbed parameterization tendencies (SPPT) scheme is one of the main methods for this purpose, and its effect is controlled by three parameters: perturbation magnitude, temporal correlation scale, and horizontal perturbation scale. There is a lack of study on the optimization of these three parameters for the operational 3-km CMA-REPS (Regional Ensemble Prediction System of China Meteorological Administration) V4.0. Based on CMA-REPS, this study selected 13 heavy rainfall cases in North China in 2024 to conduct SPPT parameter sensitivity experiments. The forecast skill for upper-air and surface variables, precipitation, and perturbation energy growth were analyzed. First, using a smaller magnitude (standard deviation equals 0.35) and dropping attenuation of the perturbations within the boundary layer most effectively enhances the forecast skill for the variables. Second, a 3-h time scale is conducive to improving forecast skill within the initial 12 hours, whereas a 6-h time scale performs better after 24 h of integration. A horizontal scale of 500 km yields the best overall performance: compared to a 1000 km scale, it improves the spread and consistency for most variables; further reducing the scale to 200 km can improve light and moderate rain forecasts within the initial 12 hours but leads to a decline in forecast skill after 18 h. Third, spatiotemporal scales significantly influence the perturbation energy growth. The 3-h time scale promotes the perturbation energy growth across scales within the initial 12 hours, while the 6-h time scale is more favorable for perturbation growth after 18 h. The 500-km horizontal scale is most beneficial for the development of difference kinetic energy and difference latent energy. Although the 200-km horizontal scale can enhance low-level perturbation energy initially and promote smaller-scale perturbation growth during convectively active periods, it results in the minimal development of larger- and meso-scale components, as well as perturbation in the mid-to-late integration period. In conclusion, the 0.35 standard deviation with unattenuated boundary layer perturbations, 6 h time scale, and 500 km horizontal scale is recommended.