Abstract: The Heilongjiang, a cold-region river spanning China, Russia, and Mongolia, is of critical importance to the ecological security and sustainable development of the basin. Thus, establishing nutrient criteria for this river is of critical importance. This study addresses the risks of eutrophication caused by agricultural non-point source pollution in the basin, as well as the basin's unique environmental effects during the ice-covered period. Using water quality monitoring data from the river's main stem from 2016 to 2024 and biological data on plankton and attached algae from 2023, three statistical analysis methods were applied: the population distribution method, the three-part method, and the reference point distribution method. The study identified the following parameters as benchmark indicators for the Heilongjiang River: pH, electrical conductivity (EC), dissolved oxygen (DO), permanganate index (COD_Mn), dichromate index (COD_Cr), five-day biochemical oxygen demand (BOD₅), ammonia nitrogen (NH₃-N), total phosphorus (TP), and total nitrogen (TN). Benchmark values were derived by analyzing the seasonal variation characteristics of these indicators and combining multiple methods.The results showed that the reference values for each indicator were as follows:pH: 7.35，EC: 15.9 ms/m，DO: 8.4 mg/L，COD_Mn: 6.0 mg/L，COD_Cr: 15 mg/L, BOD₅: 1.89 mg/L, NH₃-N: 0.28 mg/L, and TN: 0.82 mg/L; and TP: 0.047 mg/L. Additionally, a nutrient benchmark correction system was proposed for the ice-covered period. Predicted values for each indicator during the ice-covered period were obtained by applying degradation inhibition, correction factors, ion concentration effects, and biological response offset calibration. This provides a feasible solution to the challenge of applying traditional criteria in cold regions. The study established a three-dimensional technical framework that includes "seasonal differentiation analysis, ecological response verification, and multi-method collaborative calibration." This framework fills a research gap regarding nutrient criteria in cold regions. The framework provides a scientific basis for watershed ecological compensation, pollution control, and water quality management. It also provides quantitative evidence for ecological security and the precise governance of agricultural nonpoint sources in Northeast Asia. In the future, it is recommended that the China-Russia-Mongolia joint monitoring network be strengthened to enhance the adaptability of criteria to climate change.