Water film can serve as a sliding surface and cause landslides on gentle slopes. The development of “water film” in saturated sand is analyzed numerically and theoretically based on a quasi-three-phase model. It is shown that stable water films initiate and grow if the choking state (where the fluid velocity decreases to near zero) remains steady in a liquefied sand column. Discontinuity can occur in pore water velocity, grain velocity and pore pressure after the initiation of a water film. However, the discontinuity and water film can disappear once the choking state is changed. The key to the formation of water film is the choking in the sand column caused by eroded fine grains. The development of “water film ” in saturated sand is analyzed numerically and theoretically based on a quasi-three-phase model. It is shown that stable water < and grow if the choking state (where the fluid velocity decreases to near zero) remains steady in a liquefied sand column. However, the discontinuity and pore pressure after initiation of a water film The key to the formation of water film is the choking in the sand column caused by eroded fine grains.