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In order to solve the problems encountered in analyzing crop nitrogen concentration by chemical methods, such as high cost, long and complicated process, etc., a new four-waveband crop canopy analyzer was developed based on optical principle to obtain some vegetation indices to evaluate the crop growth status. The analyzer was designed to work as a wireless sensor network with a control unit and a measuring unit. As the coordinator of the whole wireless network, the controller was used to receive, display and store all the data sent from different sensor nodes. The measuring unit which consisted of several optical sensors was designed to collect, amplify and transmit the optical signals. Each sensor node contained four optical channels, which allowed the instrument work at the wavebands of 550nm, 650nm, 766nm and 850nm. Calibration test was conducted and the result showed a good performance. An experiment in maize field was also performed, and the correlation between measured N and predicted N in crop leaves had high significance with R of 0.884. Those results showed the potential of the instrument in crop nutrition level diagnosis.