The invention discloses an overall drainage construction method of an extra-large garbage dump, comprising: construction of a double-layer composite shaft and construction of a multilayer-enclosed blind ditch; the method provides vertical-transverse and deep-shallow synchronous drainage for the extra-large garbage dump. A shaft is composed of a reinforcement cage covered with spread geogrid and perforated galvanized steel pipes covered with geotextile; the shaft can function to better fix a wellhead and can drain water faster; a horizontal guide-drainage blind ditch is composed of geomembrane,inflected geogrid and perforated pipes and has good deformability and high guiding and drainage speed; by combining the horizontal guide-drainage ditch with the double-layer composite shaft, the drainage problem of a landfill can be greatly improved.