This study first analyzes the constant-voltage output principle of cascaded wireless power supply systems (CWPS) and then explores how parameter tolerances affect performance reliability through multi-scale analysis. Single-variable tests indicate that when Ct capacitors have a ± 10% tolerance, the system output power and voltage decline linearly, showing a significant negative correlation. Meanwhile, Cf capacitors have no significant impact on system performance under the same tolerance conditions. The multi-variable analysis uses full-combination simulation with 7 key resonant parameters, a ±10% tolerance, and a 5% step size, covering 78,125 combinations. The results show that first, the output power distribution is highly dispersed, but optimized combinations achieve 80.2% compliance within the ±10% power tolerance range, an improvement from the initial 71.1%. Second, system efficiency remains above 85% in most cases. However, parameter coupling leads to a long-tail distribution where 12% of combinations have an efficiency below 80%, and extreme cases can cause system failure. Third, voltage stress increases significantly, with extreme cases exceeding the nominal values by 22%. Monte Carlo simulation, which models the normal distribution of parameter errors in actual production, confirms that multi-parameter coupling amplifies performance uncertainty even with tight tolerances. The findings suggest that multi-parameter coupling reduces reliability, and design optimization should focus on adjusting parameter center values. The final optimized configuration achieves 80.5% power compliance.