In order to detect the moisture content of maize leaves quickly and nondestructively, a portable plant leaf moisture detector was developed based on near infrared spectroscopy and wireless sensor network. The structure was designed according to the principle of transmission spectrum. The device could be divided into data acquisition node and data receiving node. And the ZigBee network was used to transfer the data between them. There were three modules in the data acquisition node, including a signal acquisition module, a signal processing module and a signal transmission module. The data acquisition node mainly completed the acquisition, amplification and filtering of the spectral data, and then sent it to the PDA through the master chip JN5168. The data receiving node was designed with a data receiving module and a PDA. The signal acquisition module was the key component with a light source and a sensor. The active LED lights in near-infrared band (890nm and 980nm) sent light, and the PIN type photodiode was used to measure the transmission signal. After the signal amplification and filtering, it was sent to the data receiving node by the ZigBee network. The parameters were calculated, including T890, T980, ratio vegetation index (RVI), modified normalized difference water vegetation index (MNDWI) and so on. The field test was conducted. The correlation between the parameters and water content was analyzed. The best application location of maize leaves was recommended. The results showed that the best detecting range was 70%~80% and the resolution was 0.3%. The detection model was established by T890, T980 and MNDWI, with R2C=0.854, R2V=0.849, and root mean square error of 0.0103. It could help to detect leaf moisture content nondestructively in the field.