Abstract: In near infrared range, using low power consumption MCU MSP430 and light-to-frequency chip TSL230, a transmission water-measuring instrument was designed, which can realize non-destructive and in situ measurement of leaves. The instrument consisted of signal acquisition module, microprocessor system, software and calibration model. The signal acquisition module was made up of NIR LED, 890 nm and 980 nm interference filter, light-to-frequency chip. The light-to-frequency chip simplified the signal acquiring circuit and decreased noise disturbance. The design of hardware and software, modeling and prediction of Chinese redbud leaves water were introduced. The predicted results were identical with the real values of leaf water, and the correlation coefficient was 0.900. The main features of the instrument were higher repetitiveness, stability and reliability. Compared with other apparatus, the instrument had advantages such as small volume, simple structure, lightweight, low power consumption and anti-interference. The experiment results indicated that this system was feasible to detect leaf water non—destructively and fast on fieldwork.