Outdoor earthen sites often suffer from rainfall and floods, which leads to the formation of soil crust and changes in the physical properties of the surface soil. This process impacts the protection of the earthen sites. We used pure loess as a raw material and controlled the intensity of rainfall. By varying the length of the precipitation, we studied soil crusting under various precipitation times. We found that thickness, density and hardness of the soil crust increase rapidly with an increase of rainfall duration when the soil surface is not saturated; however, those properties increase more slowly with the increase of rainfall duration once the surface reaches saturation. At this stage, cracks quickly appear on the surface soil and form marks like concentric circles. The conclusions reached by this study may provide references for the protection of other outdoor earthen sites.