The invention provides a secondary expansion pile and a construction method thereof. The secondary expansion pile comprises a pile body, an inverted cone and an inner expansion lantern ring. An expansion section is arranged at one end of the pile body. The inverted cone is connected with a pull rope penetrating the pile body. The inner expansion lantern ring is fixed into the pile body and coincides with the upper portion of the expansion section. Inner expansion holes are formed in the side wall of the inner expansion lantern ring, and steel supports penetrating the side wall of the inner expansion lantern ring are arranged in the inner expansion holes. The inverted cone is driven by the pull rope to upwards enter the expansion section and extrudes the expansion section, the expansion section is subjected to first-time expansion, the steel supports are continuously upwards extruded, the steel supports penetrate the side wall of the inner expansion lantern ring, the steel supports extrude the expansion section again, and the expansion section is subjected to second-time expansion. Compared with an ordinary expansion pile, the secondary expansion pile has the beneficial effects thatthe expansion angle is larger, the bearing capacity is higher, sedimentation is little, stability is good, construction is simple and the manufacturing cost is low; and the secondary expansion pile is suitable for foundation strengthening of expressways, dikes, houses and other projects and spur dike protection, riverway scouring preventing, offshore hydrologic observation, mountain landslide protection and other projects.