In order to study the movement and migration of fine particles in piping of embankment foundation due to the flood transit, the sinusoidal water head was used to simulate the flood condition in the laboratory piping test of gap-graded non-cohesive soil. The piping rule under constant water head was used as the control group and the migration of fine particles during piping was tracked by the colored sand. The variation law of permeability coefficient, hydraulic gradient and the step-change of fine particle loss in samples with different content of fine particle and different pore ratio were analyzed according to the test results. The results show that under the variable water head, there is countercurrent motion in the descending section. The loss of fine particles is mainly concentrated downstream. Compared with the constant water head, variable head loses more fine particles and the migration channel runs through a larger area under the same test conditions. In addition, the larger the content of fine particles is, the smaller the pore ratio is, the larger the maximum hydraulic gradient difference is, and the more the loss of fine particles is.