Based on the PSR model and the mode of co-governance on five water categories, the indices involving sewage treatment, flood control, drainage, water supply, water conservation, and social economy were selected to establish an urban aquatic ecological security evaluation system, which was used to quantitatively analyze the status of urban aquatic ecological security. The index weight was determined by using the AHP method based on expert evaluation, and the comprehensive index method was used to calculate the status of aquatic ecological security of Linhai City. Based on the calculation results, the status of aquatic ecological security of Linhai City was evaluated. Results of the study show that the status of aquatic ecological security of Linhai City has improved under the mode of co-governance on the five water categories.