Abstract: The aim was to establish a fast and accurate determination method of the production process of L-ornithine by enzymatic conversion, and to meet the requirements of real-time monitoring of the enzymatic reaction conversion rate.The Near Infrared Spectroscopy (NIR) was applied to get the spectra of the enzymatic reaction solution, and combined with partial least squares method to establish the quantitative analysis models of L-ornithine and validated the mode.The first derivative was used to pre-treatment near-infrared spectrum, and the results of model were good accuracy and stability in the wave number 10000.0⁵500.0cm-1spectral range.The results of the model as follows, evaluation indicators of the calibration set is the best rank, R2 and RMSEP, respectively, 4, 0.9846 and 3.41, while the R2 was 0.9550 and the RMSEE was 4.47 of the validation set.The results showed that the model could be used for routine testing of enzymatic conversion and provided a simple and effective method of monitoring the enzymatic conversion of L-ornithine.