Abstract: In recent years, the online monitoring system of marine environment in China is developed from research and exploration to practical application. However, the quality of the online monitoring data, especially the nutrients data, still needs to be well improved. In order to improve the representativeness and accuracy of nutrient online monitoring data, in this study, the quality of nutrient online monitoring data from Liaohe online monitoring station was evaluated, by means of performance assessment of online monitoring equipment and contrast experiments. The results showed that the data quality of the total phosphorus from the Liaohe online monitoring station was good, with a correlation coefficient of 0.901 with the laboratory analysis data, and the significance level of double sample t test was 0.112. The online monitoring data of nutrient parameters such as nitrate, phosphate and ammonia nitrogen can reflect the changing trend of water quality of the monitoring site, but the accuracy of the data needs to be further improved.