【Objective】 The response of runoff and erosion to soil physical crust has been extensively investigated in recent decades. However, there have been few attempts to quantify the effects of the profile of soil physical crusts on erosion processes. Thus, to explore the formation mechanism of soil physical crust in microtopography, artificial simulated rainfall and stratified soil treatment method were adopted to study the distribution and characteristics of soil particle size. 【Method】 Soil plot (2.0 m long×1.0 m wide×0.5 m high) was set to a slope of 5°, filled with soil by contour tillage (20 cm ridges and 30 cm ditches). Simulated rainfall was designed for eight durations (5, 10, 12, 14, 16, 18, 20 and 30 minutes) and one intensity (100 mm h^–1). The samples were taken out by a cutting ring (diameter 10 cm) and placed in a stratified sampling device. The bottom of the device was designed with a spiral rising bottom bracket. By turning the nut, the soil sample would be rised by 1 mm after turning one circle at a time with the bottom bracket. Each tier of soil sample was stripped with a soil sampling knife. Particles of samples in each tier of soil physical crust and the collected sediment were analyzed by Mastersizer 2000. 【Result】 The results showed that: (1) During erosion, the surface sand particles of structural crust (C_st), silt-containing sedimentary crust (C_scs) and silt-free sedimentary crust (C_sfs) were dispersed, while the clay and silt particles were enriched, and the degree gradually increased with the duration of rainfall. (2) When the rainfall lasted for 30 min, from top to bottom of the profile, the content of sand and clay in C_st decreased by 4.61% and 1.73%, respectively, the content of silt increased by 1.83%. The content of sand and silt in C_scs and C_sfs increased by 29.35% and 36.59%, 4.34% and 0.39%, respectively. The content of clay decreased by 16.30% and 14.34%, respectively. (3) In the process of crust formation, the dominant factor of C_st was raindrop dispersion, the dominant factor of C_scs and C_sfs was raindrop dispersion in the early rainfall period, and sediment deposition in the late rainfall period. 【Conclusion】 Spatial location and rainfall factors were the important factors that lead to the difference in physical crust types and particle composition.