The utility model discloses a gravity farmland underground leaching solution collecting device, which belongs to the field for researching the environmental science, agrology and plant nutriology. The device comprises a leaching tray, a water outlet pipe, a liquid-collecting pipe, a vent pipe, a liquid pumping pipe, a sampling bottle, a buffer bottle and a vacuum pump, wherein the leaching tray is used for collecting the leaching solution; the liquid-collecting pipe is connected with the water outlet of the leaching tray through the water outlet pipe, the leaching solution in the leaching tray can automatically flow into the liquid collecting tube; and the vacuum pump is used for extracting the leaching solution collected by the liquid-collecting pipe to the sampling bottle through the liquid pumping pipe under the buffering of the buffer bottle. Compared with the prior art, the utility model has the characteristics of reasonable structure, convenient manufacturing, easy implementation and the like, and is particularly suitable for monitoring the influence of leaching of the soil solutes of nitrogen, phosphor, agriculture chemicals and the like on groundwater.