Abstract: To scientifically assess the aquatic ecological security status of rivers in the cold regions of Northeast China, this study took the Anzhaoxinhe River Basin as a case study. A comprehensive evaluation system was constructed, taking into account the characteristics of cold-region river ecosystems, such as multi-factor coupling and significant spatiotemporal variations. This system included 37 indicators across four categories (socio-economic impact, aquatic ecosystem health, ecological service functions, and regulatory management), incorporating specific cold-region characteristics such as flow velocity, diurnal temperature variation, and salinity-alkalinity. On this basis, the BP neural network model was introduced, and the model was trained and validated by using monitoring data from 2022 to 2023, to systematically assess the aquatic ecological security status of the basin and its key influencing factors. The research results showed that the overall habitat quality of the basin was fair (with a mean Habitat Quality Index of 111.44), water quality compliance was unstable, and the organic pollution of the bottom sediment was generally light with local and seasonal peaks. Aquatic biodiversity was low, and the community structure was deteriorating, with pollution-tolerant species being dominant. The constructed BP neural network model performed well in training and prediction (R² of the training set > 0.90, R² of the prediction set > 0.85), accurately capturing the spatiotemporal dynamics of aquatic ecological security, and demonstrating its applicability in the assessment of cold-region rivers. The river basin's ecological health status exhibited significant seasonal differences, with the best conditions in spring (88.89% of sampling sites rated as "fair") and the worst in winter (all sites rated as "fair" or "poor"). The key influencing factors were identified as the COD_Cr concentration in water and the organic matter content in sediments. This study provides a new neural network-based method for aquatic ecological security assessment in cold-region rivers and offers data and a scientific basis for the ecological management and governance of the Anzhaoxinhe River Basin.