In order to rapidly detect the nutrition content of crop, a portable multispectral detector was developed. The detector was composed of a controller and an optical sensor node, which communicated with each other through the ZigBee protocol. The optical sensor node can measure both the intensity of solar light and crop reflective light at 550 nm, 766 nm, 650 nm and 850 nm wavebands, respectively. The control unit is a PDA, in which a ZigBee wireless communication module is embedded. As the coordinator of the whole wireless sensor network, the ZigBee wireless communication module is responsible for receiving, processing and displaying the spectral data transmitted by the measuring unit. The objective of the research was to assess the agronomic performance of the detector, i.e., the accuracy of chlorophyll content estimation when using the instrument in different arable crops. Field experiments were conducted on four varieties of corn (Nongda No. 8 (G1), Zhengdan (G2), Xianyu (G3) and Jingnongke (G4)). Crop canopy reflectance was measured by the detector at jointing stage. The chlorophyll contents of sampling leaves were measured by the spectrophotometer in the laboratory. According to the typical spectral characteristics of crop and soil, the differences of reflectance between 550 nm and 650 nm ( T D ) were used to remove the soil background data points ( T D >0). Furthermore, combinations of R nir and R r ((850, 550), (850, 650), (766, 550) and (766, 650)) were used to calculate vegetation indices, including DVI, NDVI and RVI. Relationship between each vegetation index and chlorophyll content of each variety was analyzed. The results showed that the optimal parameters of G1~G4 were RVI (766, 550), DVI (850, 650), NDVI (850, 550) and RVI (766, 550), respectively, and the correlation coefficients were above 0.6. The chlorophyll content of the four varieties was clustered respectively at intervals of 0.2 mg/L, 0.5 mg/L and 0.8 mg/L. The correlation analysis results showed that the optimal resolution of the multispectral detector for detecting chlorophyll content of corn was 0.5 mg/L. The correlation coefficients of NDVI (850, 550), NDVI (766, 550) and RVI (850, 550) and chlorophyll content were 0.837 0, 0.773 7 and 0.767 7, respectively. The NDVI (850, 550) and RVI (850, 550) were selected to establish the diagnosis model with R 2 C of 0.715 4 and R 2 V of 0.684 0. The research could provide theoretical and technical support for the diagnosis of chlorophyll content of corn at jointing stage.