Abstract: Abstract: Spectral remote sensing instrument is widely used for land-use management, precision agriculture, and crop monitoring. However, these spectral sensors have some problems with expensive, complex operation, restricted by the intellectual property rights and environmental impact. In order to resolve monitoring the field growth information with characteristics of all-weather, real-time, fast and non-destructive, a crop growth information monitoring instrument based on active light source was developed based on crop growth spectroscopy. The instrument composed of the crop growth information sensor system, the control system and other units. can acquire the vegetation spectral index value of normalized differential vegetation index, ratio vegetation index, difference vegetation index and renormalized difference vegetative index are quickly and accurately. And these factors are the real-time indicators for the growth of the inversion field crops. The crop growth information sensor system includes two sensing channels of 730nm and 810nm. Each sensing channel includes light source unit and spectrum signal acquisition unit, and the light source unit sends spectrum signals of modulation to radiate crop canopy and spectrum signal acquisition unit receives information reflected for removing the sun light from crop canopy. The reflection and vegetation spectral index value of normalized differential vegetation index, ratio vegetation index, difference vegetation index and renormalized difference vegetative index were calculated. The light source unit is composed of square-wave generator, LED constant current drive circuit and optical system for light source, which exposure to crop canopy. By using active light modulation modulating technology and special optical and circuit design, the spectral information is switched to voltage information, which is easy to be obtained by hardware selection filter technology. The modulation frequency is 1 kHz. The spectrum signal acquisition unit is made up of optical system for spectrum signal acquisition, photoelectric detector circuit, the first level amplifier circuit, band filter circuit, the second level amplifier circuit and signal detector circuit, which can abstract characteristic spectrum information. The control system uses ATmega32 microprocessor as core, including key input, liquid crystal display(LCD), SD card storage, temperature and humidity sensors, sound and light alerts and power supply modules. The modularized structure is used in the design of software system based on C language, the main function of the temperature and humidity of the acquisition, supply power collection, low voltage alarm, spectral reflectance capture and storage, crop vegetation spectral index of conversion, liquid crystal display(LCD), key input and so on. The monitor can be better to remove the external interference caused by the sun in measurement process, so as to realize accurate measurement in vegetation spectral index of crop canopy. The stability experiments showed that the monitor had good stability of anti-light interference, and the output volt of monitor is almost constant, and the stability standard deviation(SD) of 730 nm and 810 nm were 1.05% and 0.47%. Wheat experiments showed that the value of vegetation spectral index measured by the monitor had significant correlation with normalized differential vegetation index, ratio vegetation index, difference vegetation index and renormalized difference vegetative index with the coefficients of determination R2 were 0.7017, 0.7071, 0.8178, 0.7804, and the root mean square error(RMSE) were 0.05362, 0.2118, 0.03434, 0.04182, respectively. Finally, the monitor has advantages as good stability, strong anti-interference capacity and easy to operate, can achieve the monitoring requirements of the field crop growth information.