Abstract: A large amount of moisture content test data of the widely graded gravel soil impervious material for Rumei Hydropower Station are analyzed. On the basis of ascertaining the moisture content and gradation of coarse and fine particles, an experimental study on the moisture content of fully graded soil materials is conducted by combining the microwave humidity method and the weighting method. The results show that the microwave humidity method can realize the rapid and accurate detection of the moisture content of finely grained soil materials below 5 mm, and the combination of the microwave humidity method and the weighting method can quickly obtain the moisture content of fully graded gravel soil materials. A comparison with the test results by the traditional drying method shows that the error can be controlled within ± 0.5%. The entire testing process can be controlled to be completed within 15 minutes, which can strengthen the quality control efficiency of the soil production process and the filling and rolling processes.