The invention relates to a tube connecting device for a heavy tube, and in particular relates to a cast tube connecting device which is matched with a novel three-station high-efficient centrifuge and has an adjustable height. The tube connecting device is characterized in that the right end of a head bracket is fixed with the top of a big arm; the left end of the head bracket is hinged with the middle of an oscillating idler wheel bracket; the lower end of the oscillating idler wheel bracket is hinged with the left end of a return spring; the right end of the return spring is hinged with theright end of the head bracket; an oscillating idler wheel is hinged with the upper end of the oscillating idler wheel bracket; a fixed idler wheel which forms a V shape together with the oscillating idler wheel, is hinged with the upper end of the head bracket; the oscillating idler wheel and the fixed idler wheel are used for supporting a cast tube; the lower end of the big arm is hinged with a big arm base; the big arm base is fixed with a tube connecting frame; the lower part of the big arm is hinged with a hydraulic cylinder; a driving arm of the hydraulic cylinder is hinged with a hydraulic cylinder base; and the hydraulic cylinder base is fixed with the tube connecting frame. The tube connecting device has the advantages that the height can be conveniently adjusted, the system rigidity is excellent and only one oscillating hydraulic cylinder is needed.