Permissible pollution bearing capacity in water function zones is crucial for managing pollution and assigning responsibility. By focusing on municipal wastewater discharge, a model was created to predict this capacity in Liquan and Jingyang counties. Results showed that pollution discharge levels were linked to river flow, with higher levels in flood seasons. COD concentrations in Liquan County exceeded water quality targets from November to March, indicating a need for reduced pollution discharge during this period. Using stable pollution concentration data in the model led to more accurate results. This study provides a scientific basis for strict water resource management.