In order to predict the nutrient content of crop non-destructively and quickly, a spectrum analyzer was developed to measure the spectral reflectance of 350-800 nm in this paper. The system has three parts: optical sensor, data transmission module and the controller. Spectral information collection software includes three modules: acquisition parameters, acquisition control and data management. Calibration experiment and application experiment were carried out to test the performance of the spectrum analyzer. The correlation was analyzed between the spectral reflectance measured by spectrum analyzer and ASD Field Spec Hand Held 2. The result showed that the average correlation coefficient value was 0.94. It was used to detect the chlorophyll and moisture content of potato. The SPAD regression model was established and the determinant coefficient R2 was 0.484, moisture content regression model was established and R2 was 0.735. Results showed that the device has a certain ability to predict chlorophyll content and moisture content of potato leaf.