Abstract: The migration of fine particles in loose soils under seepage flow can compromise the internal stability of earth-rock dams and deposits. However, previous studies on fine particle initiation have not fully considered the influence of particle characteristics on the initiation criteria. Based on the pore pipeline model, the starting force model of fine particles was established considering the particle characteristics and the effect of low stress on fine particles. By applying torque balance at the limit state, the formula of the critical hydraulic gradient for particle initiation was derived, and the reliability of the formula was verified by experiments and numerical simulation. Finally, the influences of burying depth, exposure angle, and particle size on critical starting of particles were analyzed. The results show that the critical hydraulic gradient of fine particle starting is influenced by the buried depth, exposure angle, and particle size. At shallow burial depths, exposure angle has a great influence on the critical hydraulic gradient of fine particle starting, and the influence of the exposure Angle on the critical hydraulic gradient of fine particle starting decreases as burial depth increases. With the increase of particle size, the critical hydraulic gradient for particle initiation increases gradually. This study offers valuable information for calculating the critical hydraulic gradient for fine particle initiation.