The invention relates to the field of engineering machinery, in particular to a rounded rectangular rolled steel tube for engineering machinery. The rounded rectangular rolled steel tube for engineering machinery comprises an outer connecting pipe, an inner sleeve and a fixing support, the cross section of the outer connecting pipe is in a rounded rectangular shape, the cross section of the innersleeve is circular, the inner sleeve is nested in the outer connecting pipe, the fixing support is used for fixing the inner sleeve and the outer connecting pipe, the four corners of the outer connecting pipe are respectively connected with one end of the fixing support, and the other end of the fixing support supports and is connected with the outer wall of the inner sleeve. The fixing support divides a plurality of isolation cavities between the outer connecting pipe and the inner sleeve, and the isolation cavities are filled with damping layers. The rounded rectangular rolled steel tube issimple in structure and convenient to use, and solves the problems of high self-weight and poor bearing capacity of an bearing part in engineering machinery.