The invention discloses a segment capable of being dismantled in a subway tunnel and a construction method thereof. According to the segment capable of being dismantled in the subway tunnel and the construction method thereof, the problems that a shield segment is difficult to dismantle and cannot be reused are solved. By arranging top-sealing blocks and annular segments, the segment can be dismantled in the tunnel, crushing is not required, and the segment can be reused. According to the technical scheme, the segment comprises a plurality of standard blocks forming arc-shaped structures in adjoined and surrounding modes, two adjoining blocks are closely attached to the two ends of each arc-shaped structure correspondingly, top-sealing assemblies are arranged between the adjoining blocks,and the standard blocks, the adjoining blocks and the top-sealing assemblies constitute a cylinder-shaped structure; the top-sealing assemblies comprise the top-sealing blocks and arc-shaped segments,wherein the top-sealing blocks and the arc-shaped segments are arranged between the adjoining blocks; the top-sealing blocks and the arc-shaped segments are axially spliced to jointly block gaps between the adjoining blocks, the two sides of each arc-shaped segment are both provided with wing plates, the joints of the adjoining blocks and the arc-shaped segments are provided with wedge blocks, and the wing plates and the wedge blocks are arranged in a closely-attached mode.