0.52。 In order to real-time detect the plant nitrogen content, a non-destructive crop growth analyzer is developed. It is made up of a sensor and a controller. The optical part of the sensor is made up of four optical channels and four photodiodes. Two channels receive the sunlight and the other two receive the reflected light from the crop canopy at the wavebands of 610nm and 1220nm. The circuit part of the sensor is made up of power supply unit, amplifying unit and a wireless module. The controller has functions such as keyboard input, LCD display, data storage, data upload, and so on. Calibration tests show that the optical part has a high accuracy and the wireless transmission also has a good performance. The field tests comparing with a commercial spectrometer (Quality Spec made by ASD Co.) also show an acceptable correlation of 0.52.