When the doublewavelength method is applied to detect nitrate nitrogen, its prediction accuracy is affected by the superposition of absorbance of organic pollutants. To solve this problem, one kind of method based on agent parameters is proposed. The six integral area values contained in the hybrid spectrum are used as the agent parameters. The demarcation point of the agent parameters is determined by the dynamic segmentation algorithm of the fourth derivative spectrum. Each agent parameter at the demarcation point is obtained by the area integral method. According to the ratio of organic pollutants agent parameters, their contribution degree for the hybrid absorption spectrum before the demarcation point is obtained. By using the preprocessed data, the least square method is used to formulate the prediction model for nitrate concentration and its integral area. This model is applied to the practical water sample detection. Compared with the traditional dualwavelength method, experimental results show that the determination coefficient of the model is 09998 and the average standard deviation is less than 3%. It can also realize lower detection limit (≥0009 mg/L), better recovery (95%~104%) and wider linear range, which provides reliable technical support for the accurate detection of nitrate nitrogen in water samples.