The utility model discloses an assembled steel construction conversion layer of tower crane sets up on lattice formula tower machine basis, and this assembled steel construction conversion layer of tower crane includes equipment girder steel and supplementary girder steel, the equipment girder steel with supplementary girder steel is each two, one of them root supplementary girder steel level sets up on the lattice formula tower machine basis, and with lattice formula tower machine basis is connected, another root supplementary girder steel level sets up the top on lattice formula tower machine basis, the vertical setting of two root device girder steels is in between two supplementary girder steels, and be parallel to each other, the equipment girder steel with the whole that supplementary girder steel constitutes is " II " style of calligraphy. The utility model provides a steel construction conversion layer is constituteed through four simple shaped steel, and its wholeness and stability are good, has stronger antidumping and the ability of resisting the impact, makes basic atress make clear safe and reliable, and construction cycle is short, and just circulated use of easy dismounting has certain advance in time limit for a project, safety, in the aspect of energy -concerving and environment -protective etc..