Nitrogen is one of the necessary nutrient elements for crop growth and products,and the monitoring of crop nitrogen nutrition by the real-time,rapid,non-destructive and accurate way is of significance in estimating crop growth parameters,enhancing nitrogen use efficiency,reducing farmland contamination from excessive use of fertilizer nitrogen. The mechanisms of non-destructive monitoring of crop nitrogen nutrition are investigated by spectroscopy and eco-physiological bases. The theoretical basis and method the obtaining the crop nitrogen-specific spectra information are shown,and the portable nitrogen non-destructive monitoring spectrum instrument for crop is designed and manufactured. Based on the data from rice in field,the instrument is tested and evaluated. The results show that the instrument worked stably and finely,which is very suitable to the nitrogen non-destructive monitoring for crop in field.