The invention relates to a cofferdam formed by latched steel tube and concrete combined piles and a construction method. The cofferdam comprises base sealing concrete, a plurality of latched steel tube piles, anchoring piles and an inner support, wherein the lower parts of the latched steel tube piles are sleeved with the anchoring piles; the base sealing concrete is arranged at the top of bed rock; the latched steel tube piles are inserted into the edge of the base sealing concrete and are sequentially connected end to end; each anchoring pile is prepared from reinforced concrete and deeply extends into the bed rock; each latched steel tube pile comprises a steel tube main body, a connecting pipe and a T-shaped connecting part; the inner support comprises a first inner support waist beam and a plurality of second inner support waist beams, wherein the first inner support waist beam and the second inner support waist beams are arranged in sequence from top to bottom. The cofferdam disclosed by the invention has the advantages of realizing dry excavation, solving the problems of difficult underwater blasting excavation and uncontrollable blasting excavation work amount, also solving the problem of relatively large difficulty in quality and safety control, also reducing the use amount of steel and reducing the underwater blasting volume; meanwhile, cofferdam construction and pile foundation construction can be synchronously performed, so the construction cost is lowered, and the construction period is shortened.