The invention provides a bracket and a construction method of a deep trench support so as to solve the problem that the bracket is inconvenient to mount and cannot be repeatedly utilized in the construction process of the deep trench support. Due to the arrangement of a suspending device at the upper part of the left flange of an I steel, when the bracket is mounted, the mounting of the bracket can be finished as long as the bracket is fixed at the top of a steel sheet pile wall through the suspending device, so that unnecessary construction steps, such as welding, are avoided, and the problem of construction inconvenience caused by welding necessity during the mounting of the bracket is solved. As the bracket can be conveniently disassembled after the construction of the deep trench support is finished, the bracket can be cyclically used, and the problem that the existing bracket cannot be repeatedly utilized is solved.