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Abstract. The chlorophyll content is one of important parameters to evaluate the growth status of the crop. According to the spectrum response of chlorophyll content, it is a fast and non-destructive method to access the growth information by using spectral reflectance measurement. Thus, a multi-spectral information acquisition system was developed to measure the reflectance from crop canopy based on the multi-rotor UAV (Unmanned aerial vehicle) platform. The system was designed including a multi-spectral sensor and a ground-based monitoring system, in which the sensor could be equipped on a multi-rotor UAV platform and the wireless sensor network was used to transmission the data between the UAV and the ground-based station. Firstly, the sensor was designed and developed following the optical structure unit, photoelectric detection circuits, and transfer and control units. According to the characteristics of crop canopy and the actual requirements of UAV operating environment, the optical multi-channel was made with optical filtering technology to improve the signal-to-noise ratio of light radiation information input. The sensor with six optical channels could collect spectral reflectance of crop canopy at 450, 550, 650, 766, 850 and 900nm. A GPS module was used to realize the sampling position. Secondly, the ground-based monitoring system was developed based on Baidu Map and Visual Studio 2017 development environment. The system was designed including data receiving module, data displaying module, data storing module and positioning module. The optical performance of the sensor under different light conditions was tested by using optical integrating sphere. After the calibration, the correlation analysis multi-spectral sensor and optical integrating sphere shows that the correlation coefficient values are 0.97, 0.91, 0.92, 0.91, 0.97 and 0.97 respectively. The system provides a support for the on-line crop monitoring in the future.