Abstract: Moisture content is an important index of cohesive soil.For the purpose of rapid detection of moisture content in cohesive soil, based on the principle of microwave humidity method, the Hydro-Probe IV microwave humidity sensor was selected.The detection principle of the instrument was analyzed, and the calibration method and the steps of detection method were proposed.According to the influence of soil type and soil sample quality on test results, corresponding solutions were proposed.A quasi-static screw type soil sample density control device was developed to reduce the influence of compactness on the results.The fitting effect of the calibration curve was measured by the determination coefficient, correlation coefficient and the sum of squares of mean square residuals.Moisture content test by this device was carried out using conventional clay soil, and the accuracy of the test results was analyzed by using the absolute error, the sum of squares of mean square deviation, the correlation curve between the results of the microwave humidity method and the drying method, which confirmed that the test result had high precision.The reliability of the test method was analyzed based on the t-test method, and the test time was counted.The results showed that accuracy of the method can met the specified requirements, and the reliability can achieved 95%.Calibration can be completed in advance, and two parallel measurements was only need 10～12 minutes, proving that the detection time is short, and it can achieve the goal of rapid detection of moisture content of cohesive soil.