The invention relates to the construction field of underground engineering, in particular to a construction method of a movable side wall of a large overall template of a large-span deep foundation pit. The invention solves problems that the conventional construction method of the side wall of a deep foundation pit has the disadvantages of large volume of the work, high labor intensity, difficulty of guaranteeing the quality of construction, long construction time and the like. The construction method comprises the following steps of: excavating the deep foundation pit and mounting the steel support, constructing the cushion layer and the main structure of the soleplate, dismounting the steel support, performing the waterproofing work of the side wall and constructing the reinforcing steel bar, designing the whole length and the height of the large overall template according to the detachable support space of the side wall and the height of the main side wall, aligning the large overall template via a mobile mould frame, concrete construction of the side wall and then demoulding; moving the overall template forwards in time via the mobile mould frame and repeating the steps to construct the side wall of the next section. The construction method of the invention has the advantages of high construction speed, few construction joints, high construction quality, safe construction,low labor intensity, no consumption of scaffold and small overall investment. The construction method is suitable for constructing the side wall structure of the underground engineering and various barrier walls.