Abstract: Epiphytic algae are important indicators of the health of watershed water environments.In summer (June-August) and fall (September-November) of 2023, 30 sections were set up in the main stream of Heilongjiang River from west to east to investigate the living algae and water environment quality. 234 species of living algae were found in Heilongjiang River, belonging to 7 phylums and 95 genera, which are diatoms-green algae-cyanoalgae type of water bodies.The Heilongjiang P-IBI indicator system constructed by analyzing the distribution range, discriminative ability and Pearson correlation of 17 candidate biological parameters. The results showed that the average P-IBI score for the Heilongjiang River was 0.594 in summer and 0.886 in fall, and the health status of the river was “good”. The correlation thermograms showed that the environmental factors that mainly affected P-IBI in summer and fall were conductivity, and water temperature, respectively. Most of the results of the biological integrity index of living algae were consistent with the water quality condition evaluated by WQI, indicating that the P-IBI method can better reflect the health condition of the river, but the permanganate index and chemical oxygen demand of the water quality index reached the standard of surface water class IV, which should be given key monitoring to prevent the eutrophication of the river water body.