The invention provides a steel reinforcement cage of an oversized-diameter engineering pile and a construction method of the steel reinforcement cage. The steel reinforcement cage comprises a first longitudinal bar layer, a second longitudinal bar layer and an inner longitudinal bar ring. The first longitudinal bar layer is located on the outmost layer, attached to the inner wall of a hole and formed by arranging a plurality of steel bars in the longitudinal direction at intervals to form a circle. The second longitudinal bar layer is close to the inner surface of the first longitudinal bar layer and is formed by arranging a plurality of steel bars in the longitudinal direction at intervals to form a circle. The inner longitudinal bar ring is arranged in the second longitudinal bar layer and formed by arranging a plurality of steel bars in the longitudinal direction at intervals to form a circle, and the radius of the inner longitudinal bar ring is half that of the first longitudinal bar layer. The first longitudinal bar layer and the second longitudinal bar layer are fixed by inner stirrups and outer stirrups, and the structure is stable; the inner longitudinal bar ring is provided with fixing inner ring welding bars and locating inner ring steel bar fixing bars, and deflection of the inner longitudinal bar ring is avoided; and the whole steel reinforcement cage can completely adapt to application of the oversized-diameter engineering pile. According to the construction method, the whole steel reinforcement cage is built step by step from outside to inside and from bottom to top, the building efficiency is improved, and meanwhile the construction safety of construction personnel is guaranteed.