Abstract: Aiming at the problem of inaccurate detection of the nitrate nitrogen solution concentration with interfering substances in ultraviolet spectrophotometry (UV method), a nitrate nitrogen concentration detection method based on principal component analysis (PCA) and BP neural network was proposed. First, the absorbance of the nitrate nitrogen reagent at 196 nm~631 nm was measured by the material composition detection system of the micro-spectrometer, which was divided into test set and training set. Then, the PCA was used to calculate the training set to obtain the principal components. Finally, a three-layer artificial neural network was built based on the BP algorithm. The obtained principal components were divided by 8 and input into the network for training. During the training, the leaving-one method was adopted for cross-validation. This model was used to calculate the training set and test set, the mean relative error between the obtained results and the true concentration is 2.411 5% and 1.553% respectively. The experimental results show that the method can better detect the concentration of the nitrate nitrogen reagent with interfering substances.