The invention provides an underground water decompressing-draining device and an underground water decompressing-draining system, and relates to the field of infrastructure water draining facilities. The underground water decompressing-draining device comprises a water filtering assembly, a water guiding device and a water draining assembly, wherein the water filtering assembly is used for filtering underground water; the water guiding device is used for storing the underground water filtered by the water filtering assembly; and the water draining assembly is used for draining the stored underground water when the water pressure of the underground water stored in the water guiding device is too high. By adoption of the underground water decompressing-draining device provided by the invention, underground water can be stored everywhere; when too much underground water is stored, the stored underground water can be drained out; and then the infrastructure can be effectively protected. The invention further provides the underground water decompressing-draining system comprising the above underground water decompressing-draining device.