The invention relates to a joint structure with a steel support serving as a steel replacement support and a construction method. The joint structure is arranged in a side wall between the end of the steel support and an underground diaphragm wall, the joint structure comprises a first connecting piece used for connecting the underground diaphragm wall and a second connecting piece fixed with the first connecting piece, and the second connecting piece abuts against the end of the steel support. According to the joint structure arranged between the underground diaphragm wall and the steel support, the technical problem that in the prior art, the construction process of a supporting structure in supporting construction of a deep foundation pit is tedious is solved, and the tedious process that when side wall construction is conducted, the steel support needs to be dismantled, then side wall construction is conducted, and then the steel replacement support is adopted for supporting is solved; and according to the joint structure, by adjusting the construction form of the opposite supporting parts at the two ends of the steel support, the joint structure can be used as the steel replacement support at the same time, secondary construction of the steel replacement support is avoided, the construction period is greatly shortened, large investment of manpower, materials and machines is reduced, and meanwhile the safety of the foundation pit can be guaranteed.