Abstract: A heavy load elevator installation platform capable of stretching and retracting steplessly, which includes an upper beam assembly and a lower beam assembly that can realize stepless stretching and retracting. The upper beam assembly includes an upper beam left C steel, upper beam middle C steel, and upper beam right C steel connected end to end in sequence. A plurality of long holes formed at an inclined included angle with the horizontal are formed in the inner side walls of each of the upper beam left C steel and the upper beam right C steel. A plurality of long holes are respectively formed in the two side surfaces, facing the upper beam left C steel and the upper beam right C steel, of the upper beam middle C steel. The structure of the lower beam assembly is the same as that of the upper beam assembly.