Abstract: This paper systematically analyzes a large amount of moisture content and grading test data of the wide graded gravel soil impervious material for the 315m world's highest earth rock dam of Rumei Hydropower Station on the Lancang River in Xizang. On the basis of mastering the moisture content and grading laws of coarse and fine materials, this paper conducts an experimental study on the moisture content of fully graded soil materials 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 fine grained soil materials below 5mm, and the combination of the microwave humidity method and the weighting method can quickly obtain the moisture content of fully graded gravel soil materials. Compared with the traditional drying method test results, the error can be controlled within ± 0.5%, and the accurate P5 content of soil materials can be obtained. The entire testing process can be controlled to be completed within 15 minutes. Combined with automation improvement, the testing efficiency can be further improved, which can strengthen the quality control efficiency of the soil production process and the filling and rolling process.