The invention discloses a lock catch steel pipe and reinforced concrete composite pile cofferdam which comprises bottom sealing concrete, lock catch steel pipe piles and reinforced concrete piles. The lock catch steel pipe piles are anchored in the edge of the bottom sealing concrete and are sequentially connected end to end. The bottom of each lock catch steel pipe pile is at inserted into the bottom sealing concrete by 50 cm. The upper portion of each reinforced concrete pile is in cup joint to the lower portion of the corresponding lock catch steel pipe pile. The lower portion of each reinforced concrete pile is anchored into the bottom sealing concrete and exceeds the bottom of the bottom sealing concrete. Multiple steel purlins are arranged in an area defined by the multiple lock catch steel pipe piles from top to bottom. An inner support is mounted on each steel purlin. A longitudinal supporting rod is arranged between every two adjacent layers of inner supports. According to the lock catch steel pipe and reinforced concrete composite pile cofferdam, the problems that underwater blasting excavation is hard, and the blasting excavation work amount cannot be controlled are solved; due to the fact that reinforced concrete anchoring piles are designed in the lock catch steel pipe piles, the anti-floating capacity of the cofferdam is increased, the thickness of the bottom sealing concrete is reduced, and the milling groove work amount is reduced; and meanwhile the construction cost is reduced.