Construction method of movable gantry in construction of big cantilever bent cap

The invention discloses a construction method of a movable gantry in a construction of a big cantilever bent cap. The construction method is characterized in that aiming at the construction of the big cantilever bent cap, a movable gantry system is set, wherein the movable gantry system comprises three units of a left side unit, a middle unit and a right side unit respectively, the left side unit and the right side unit have symmetrical structural forms and are composed of two groups of independently set movable gantries respectively, and the distance between the two groups of the movable gantries is the width of a motor way which maintains normal traffic; movable universal wheels are adopted as trundles of the movable gantries, a helix tube is adopted by the middle unit as a bearing stand column, the top of the helix tube is provided with a sand box, a distributive girder is arranged on the sand box, and a Bailey girder which is used for paving bent cap bottom board is supported on the movable gantry system.