The invention relates to a triangular concrete thin-wall folded plate pile; end-to-end connection is conducted on a concrete left plate, a concrete middle plate and a concrete right plate so as to bend and form a triangular drum shape; the three angles of the triangular drum are respectively provided with a first bottom angle joint-pouring concrete zone, a second bottom angle joint-pouring concrete zone and a top angle joint-pouring concrete zone which cover part of steel bars of a steel bar mesh. A preparation method comprises the following steps: the concrete left plate, the concrete middleplate and the concrete right plate which are flatly horizontal are simultaneously poured and stretched to form a concrete flat plate of which three steel bar meshes are connected; the concrete left plate and the concrete right plate are symmetrically bent to form an angle; when the angle reaches 90 degrees, harsh concrete is adopted to cast the bottom angle joint-pouring concrete zones; the symmetrical bending is conducted continuously so as to lead the concrete left plate, the concrete middle plate and the concrete right plate to form a triangular drum shape; short connecting bars on the toppart are welded, the top angle joint-pouring concrete zones are cast, simultaneously adjustment and repairing are conducted on the bottom angle joint-pouring concrete zones, and when the joint-pouringconcrete reaches design strength, the triangular concrete thin-wall folded plate pile is formed.