The invention discloses an anchor foundation pit drainage system and a construction method thereof. The anchor foundation pit drainage system adopts a multistage drainage system structure, and comprises a pit top drainage structure, a slope drainage structure and a pit bottom drainage structure; the pit top drainage structure comprises a intercepting ditch and a water retaining wall; the slope drainage structure is arranged on a peripheral slope of a foundation pit, and comprises a drainage pitch and a water pipe; the pit bottom drainage structure is positioned at the bottom of the foundationpit, and comprises a water gathering ditch and a water collecting well; different drainage structures are arranged in each layer of structures according to specific structures; all the drainage structures are combined to form one complete drainage system; and the whole system is simple in structure. The invention further discloses a construction method of the anchor foundation pit drainage system;each grade of the drainage system is constructed one by one through a construction mode from top to bottom; construction is simple, stable and reliable; drainage is smooth; and the effects of damp prevention and drainage are achieved.