Lock catch steel pipe pile cofferdam construction and inner support stress adjusting method

The invention discloses a lock catch steel pipe pile cofferdam construction and inner support stress adjusting method which comprises the steps that a steel casing in a cofferdam construction area is lengthened firstly, and a lowering system is installed at the top of the steel casing; the upper inner supporting structure is integrally assembled on site, and the lower inner supporting structure is assembled on site in a scattered mode. Then the upper inner supporting structure is placed to the designed elevation, a supporting piece is arranged on the outer side of the steel casing, and the supporting piece supports the upper inner supporting structure; steel pipe pile inserting and driving construction is conducted along the outer side of the upper inner supporting structure, and a cofferdam structure is defined by the multiple steel pipe piles; water pumping is conducted on the inner side of the cofferdam structure, the lower surrounding purlins are arranged on the inner side of the cofferdam structure in a