A soil drainage device includes a host, at least one water collecting assembly and a piping unit. The host includes a host housing for receiving a control module and an air pump. The water collecting assembly includes an assembly housing defining a water collecting chamber and a water reservoir chamber, and having an upper penetrating bore and a plurality of openings for entering of water into the water collecting chamber through a filter unit. The water flows into and is stored in the water reservoir chamber. At least one air conducting pipe is disposed to introduce compressed air from the air pump into the water reservoir chamber to form a pressure so as to force water flow out of the water reservoir chamber through a water draining pipe.