In order to realize rapid and real-time detection of available nitrogen in coco-peat substrate, a detecting instrument based on near infrared (NIR) diffuse reflectance spectroscopy was designed. The hardware system of this instrument mainly consisted of pretreatment device, pneumatic conveyor, gravity settling sample chamber, near infrared spectrum detection device, sample recovery device and air compressor. Totally 135 samples of coco-peat substrate with different available nitrogen contents were prepared. Original spectral data of these samples were obtained by the hardware system of the developed instrument. An optimal partial least squares regression model for predicting available nitrogen content of coco-peat substrate was established. The corresponding correlation coefficients of correction set and validation set were 0.973 and 0.965, respectively;the root mean square errors of correction set and validation set were 14.025mg/(100g) and 15.757mg/(100g), respectively;and the residual prediction deviation was 3.72. Based on the MFC development tool, the software interface of hardware control and realtime detection and analysis of the instrument was developed in C/C++ language. The optimal coco-peat substrate available nitrogen prediction model established was built into the software, and the functional hardware control and available nitrogen NIR spectroscopy detection was realized by one-button operation. The test results showed that the correlation coefficient between the predicted value of the developed instrument and the measured value of national standard was 0.883, and the root mean square error was 18.605mg/(100g). The instrument can realize the rapid and realtime detection of available nitrogen in coco-peat substrate, and the prediction performance was good, which can meet the actual needs of rapid evaluation of coco-peat substrate fertilizer.