[Objective] The dynamic process of erosion evolution of granite weathered soil under the action of changing hydrodynamic head was determined to study the influence of dynamic hydraulic conditions on the development of internal erosion of soil, and to define the particle migration law and internal erosion mechanism, in order to provide a theoretical basis for the in-depth study of the destruction mode and slip-promoting mechanism of granite slopes. [Methods] A vertical soil column seepage device was designed to carry out seepage tests on granite-weathered soil columns under rising hydrodynamic head and sinusoidal head conditions. Based on the test observations at the top and sides of the seepage soil columns, the developmental characteristics of the internal erosion of granite weathered soils under the action of changing hydrodynamic head were analyzed in terms of the changes in seepage velocity, the amount of soil particles lost, particle gradation, and quality of the particles before and after seepage. [Results] ① Granite-weathered soil had large differences in particle size, and there were small pores in the soil matrix. Seepage and scouring effects transported soil particles through the pores in the soil matrix. The amount of fine particles lost through internal erosion was relatively large, and the amount of coarse particles lost was small. ② Internal erosion was a gradual development process, and the soil structure in the weak areas of the soil was the first to exhibit deformation and damage. In the test, the seepage springs progressed from the boundary of the soil column to the middle area of the soil column, and the seepage channels developed from bottom to top along the seepage direction. Significant changes in the hydraulic conditions within a short period of time resulted in rapid penetration of the seepage channels. ③ Internal soil erosion will stabilize with seepage time, but a sinusoidal hydrodynamic head will activate the movement of soil particles and intensify internal soil erosion. Increasing the magnitude or decreasing the period of the head change can increase the internal erosion of soil, resulting in faster water transport and increased loss of particles through migration. [Conclusion] Changes in hydraulic conditions had a significant effect on erosion within the soil, with sinusoidal heads exacerbating particle migration and loss.