Abstract: The drying method is a commonly used method in the determination of loess moisture content. The laboratory uses oven drying method. At the engineering site, the microwave ovens are commonly used for drying in order to save time. There is no uniform standard for the best time to dry in a microwave oven. In this paper, the drying of loess and red clay in Yan'an area has been carried out by microwave oven. The moisture content of soil samples with different drying time has been compared, and then the drying time for the moisture content of soil samples reached stability has been determined. The results show that, when the microwave oven is set to high firepower, the drying time is 7 minutes for Yan'an Q3 loess, 8 minutes for Q2 loess, and 10 minutes for red clay in N2b-j group. This result can be used as a reference for rapid determination of moisture content of loess and red clay at the site of engineering construction and geological survey.