Abstract: The calculated total outflow from Gezhouba Reservoir substantially exceeds the discharge released by Three Gorges Reservoir. This volume discrepancy surpasses the natural inflow contribution from the inter-reservoir reach, necessitating immediate outflow recalibration. To accurately calculate outflow of Gezhouba Reservoir and maintain hydrological equilibrium between the Three Gorges-Gezhouba cascade reservoirs, we employed the SCE-UA optimization algorithm with the inflow-outflow water balance as the calibration criterion. Seasonally varying, head-dependent correction coefficients were developed to rectify turbine-specific discharge allocations. Flood season results demonstrated a reduction in mean absolute discharge deviation (MAD) from 1 720 to 571 m³/s, with monthly volume deviations decreasing from 4.318 to 0.109 billion m³. Corresponding non-flood season improvements showed MAD reduction from 1 650 to 745 m³/s and volume deviation decreased from 452 to 253 million m³. The water balance-based discharge correction framework significantly enhanced outflow quantification accuracy, effectively mitigated systemic water balance errors, and provided reliable hydrologic data for cascade reservoir operations.