The invention relates to the technical field of immersed tube tunnels, in particular to a steel cap installation method. The installation method comprises the steps that a steel cap is divided into aplurality of sections, and the sections are hoisted from bottom to top in a left-right symmetrical mode; and the hoisted-in-place sectional steel caps are positioned and welded. According to the steelcap installation method, the steel cap is divided into the sections for being installed, so that the steel cap is conveniently transported and hoisted, and the construction difficulty is greatly reduced; the construction efficiency is improved, and the construction risk is also reduced; the sections are hoisted from bottom to top, the firstly-installed steel cap is conveniently positioned and adjusted, it is ensured that the steel cap has the high precision, so that the late-installed steel cap also has the good precision, and it is ensured that design requests are met after the steel cap iswholly hoisted; and meanwhile, the bottom plate section of the firstly-hoisted steel cap supports the sections of the late-hoisted steel cap, and the subsequently-installed sections are conveniently constructed.