The invention relates to a telescopic magnetic jackstay. In order to overcome the defects of an existing telescopic jackstay, the telescopic magnetic jackstay is designed by utilizing the magnetic spring principle. The telescopic magnetic jackstay comprises an inside-sleeved type magnetic spring, a piston and a piston rod, wherein the inside-sleeved type magnetic spring is composed of a piston cylinder and at least two sets of magnetic elements, the magnetic elements are arranged in the piston cylinder and can move in the axial direction of the piston cylinder, the piston is arranged in the piston cylinder, and one end of the piston rod is fixedly connected with the piston. The telescopic magnetic jackstay is characterized in that the head end and the tail end of the piston cylinder are provided with end sockets, wherein the end socket at the head end of the piston cylinder is provided with a hole, and the piston rod extends out of the hole; the inner side of the end socket at the tail end and the end faces of the piston are fixedly provided with soft iron sheets, and the magnetic elements located at the two ends in the piston cylinder are connected to the inner side of the end socket at the tail end and the end faces of the piston respectively through the soft iron sheets in a magnetic-adsorption mode. Compared with the prior art, the telescopic magnetic jackstay has the advantages that the structure of the telescopic magnetic jackstay is simple; the support force of the telescopic magnetic jackstay is equivalent to the support force of a pneumatic jackstay, outclasses the support force of a spring jackstay and is convenient to adjust; besides, the requirement for machining accuracy is low, cost is low, adaptability to environment is high, and service life is long.