High-accuracy measuring system of soil temperatures was designed. Thermocouple was used as temperature sensors. Under the control of the micro-controller, high-accuracy and automatic detection was achieved to analyze the impact of soil temperature on water and heat of soil. The system was studied from three aspects, such as hardware circuit, software and curve fitting. By using the electric bridge method for temperature acquisition, least squares method was used to piecewise fit samples values and temperature. Their relationship curve was described. The measurement error was compensated and corrected to ensure the measurement precision. The result showed that the experimental absolute error was less than 0.02℃.