Behind-membrane draining device and method suitable for geomembrane seepage prevention

The invention relates to a behind-membrane draining device suitable for geomembrane seepage prevention. The device comprises a first geomembrane arranged on a dam body, wherein an opening hole is formed in the first geomembrane; reverse filter geotechnical cloth is arranged below the opening hole; the size of the reverse filter geotechnical cloth is greater than that of the opening hole; a second geomembrane coats the opening hole; the size of the second geomembrane is greater than that of the opening hole; the top end of the second geomembrane is connected with the first geomembrane; a cover plate is placed on the second geomembrane. The behind-membrane draining device is good in seepage prevention effect, simple in structure and low in manufacturing cost, and has wide application prospect.