Abstract: The problem of piping has gained widespread concern in hydraulic engineering. Usually, the researches on the piping are based on the steady flows. Under the function of unsteady flows, the variation of water level is different from that in the case of steady flows. The transformation rate of water potential that active momentum imposes on soil particles differs from that in steady flows, leading to the difference of the law of soil piping from the situation of unsteady flows. According to the calculation of theoretical formula, the hypothesis that water head of soil piping destruction under unsteady flows is lower than that under the steady flows is confirmed, and it is also pointed out that the migration law of soil particles has great randomness in a small area during the experiment. The experiment is designed based on the theoretical studies. By controlling water head, the piping tests on the soil samples under the situation that the water head changes in approximate sine curve are carried out. The correctness of theoretical analysis is verified by monitoring permeability changes of each part within the samples.