Abstract: Using some soil moisture and rainfall data in Jianli county and Fang county, the unreasonable values of the correction coefficients of the two stations were diagnosed and analyzed. According to certain rules, the initial value range of the threshold value of the two coefficients A₀ and A₁ were determined. According to the observation data of artificial soil moisture in Hubei province over the years, the “volatility of volumetric moisture content” at different levels was calculated. Interpolate the CLDAS soil volumetric water content hourly simulation grid data for one and a half years to 46 automatic soil moisture sites and 8 levels in Hubei province. Calculate the correlation coefficient r2 between the instrument measured value and the CLDAS of all the observation stations （layers） hourly volumetric water content and the correlation coefficient r1 between the instrument measured value and the final value. Picking the data with r1>0.8, r2>0.6 and the final value of the volumetric water content within the “volatility range of volumetric water content” as a basis to obtain the empirical value ranges of the two coefficient thresholds in Hubei province. The negative value of A₁ violates the working principle of the DZN series of soil moisture stations, and A₁ cannot be too small. In general, the initial value range of the two coefficient thresholds were A₀ （-36, 36） and A₁ （0.1, 10）. The empirical value range of the two coefficient thresholds in Hubei province was reduced to A₀ （-20, 35） and A₁ （0.25, 1.57）. In the field calibration method, ensuring the true reliability of the soil bulk density value as a constant can reduce the error in calculating the correction coefficients A₀ and A₁.

Key words: automatic soil moisture station, volumetric moisture content, correction coefficient, threshold value, Hubei province