Highly telescopic hydraulic support for low coal seam

The invention discloses a highly telescopic hydraulic support for a low coal seam, which comprises a base, a top beam and a shield beam, wherein two upright posts are symmetrically arranged between the top beam and the base, and two balancing jacks are symmetrically arranged between the top beam and the shield beam hinged with the top beam; a front connecting rod and a rear connecting rod are respectively hinged between the shield and the base, the middle part of the base is provided with a push jack, and the push jack is hinged with a push rod; an axial slotted hole is arranged in the wall of a middle cylinder of the upright posts, an upper opening and a lower opening, which are communicated with the slotted hole, are arranged in the internal wall and the external wall of the middle cylinder, the upper opening is communicated with the upper cavity of the middle cylinder, and the lower opening is communicated with the upper cavity of an external cylinder; the rear part of the base is provided with two free po