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A near infrared reflection (NIR) soil water sensor was developed for rapid measurement of soil moisture content. Light emitting diodes (LEDs), at 1940nm and 1800nm respectively, were used as measurement and reference light sources. The photodiode received the light reflected from the soil surface to produce an output electronic signal, which was related to the soil moisture content. The received signals were put into a two stage pre-amplifier, an analogue/digital (A/D) transfer, and then were displayed and stored. A certain relationship was found between the output reflected light and soil moisture content. The experiment results showed that the distance from light sensor to soil surface had some influences on the intensity of received signal. According to the sensor structure, a certain distance could be chosen to make a better intensity and stability of reflected signal. The reflectance of the two light sources decreased with increase of soil particle size. There was a strong linear correlation between the relative absorption depth and soil moisture content, and the determination coefficient was 0.863.