The invention discloses a construction method for temporarily supporting and strengthening a reinforced concrete structured beam by using a steel column. The method for temporarily supporting and strengthening the reinforced concrete structured beam is finished by the following construction steps of: arranging a base steel plate of the steel column; stringing a bolt hole to draw and lift steel column members; adjusting the verticality of the steel column and limiting the position; arranging and fixing a steel column jacking support; tightening and prepressing the steel column by using a simple jack, welding to form a steel column bearing base support, and the like. The construction method has the advantages of simple assembly and disassembly, low labor intensity, low labor and material consumption, and good effect of the formed temporary support structure.