Assembly-adjustable steel stair

The utility model discloses an assembly adjustable steel stair which comprises two groups of symmetrically arranged stair beam assemblies, a plurality of step plates arranged between the two groups of stair beam assemblies and handrail assemblies arranged on the stair beam assemblies, lower mounting parts are arranged at the bottoms of the stair beam assemblies, and upper mounting parts are arranged at the tops of the stair beam assemblies. The handrail assembly is detachably connected with the ladder beam assembly; the two ladder beam assemblies are the same in structure and each comprise a first rectangular square tube ladder beam and a second rectangular square tube ladder beam which are arranged in parallel, the bottom ends of the first rectangular square tube ladder beams and the bottom ends of the second rectangular square tube ladder beams are rotationally connected with the lower mounting parts, and the top ends of the first rectangular square tube ladder beams and the top ends of the second rectangul