The invention discloses a water-air two-phase flow simulation experiment device for a two-layer medium. The device comprises a simulation tank, wherein the simulation tank is divided into three cavities including surface water simulation cavities in two sides and a simulation box; the simulation box is filled with a strong-seepage medium and a weak-seepage medium from bottom to top, a plurality of observation tubes and insertion tubes are arranged on the outer wall of the simulation box in one-to-one correspondence, the bottom of each observation tube is communicated with the corresponding insertion tube through a hose, and the insertion tubes are located in different positions of the side surface of the strong-seepage medium. The insertion tubes are inserted into the strong-seepage medium above the ground water level for pressure change observation, and the insertion tubes at the middle-lower part facilitate observation of ground water level change; lifting devices are mounted outside the simulation tank, and fixed-water-head overflow boxes are arranged on the lifting devices to control the surface water level, a tracer filling tube is arranged in the strong-seepage medium, and ascending rules of capillary water are observed. According to the water-air two-phase flow simulation experiment device, the air pressure in a vadose zone is measured according to the stabilized water head differences of U-shaped piezometer tubes, change rules of the air pressure along with time is captured, and the dynamic features of the ground water level after the pressure change are observed according to the water level change of ground water level observation tubes, and the water-air action mechanism is researched.