The invention relates to a shield segment and a construction method thereof, in particular to a segment form for preventing upward floating of a shield tunnel and a construction method of the segmentform. A plurality of segment ring units are sequentially arranged in the extending direction of the shield tunnel, and each segment ring unit is formed by a plurality of segments which are spliced andenclosed, wherein one of the segments serves as a top sealing segment; and the top sealing segments are provided with grouting holes correspondingly, and two anti-floating pieces are mounted every the top sealing segment of the corresponding segment ring unit correspondingly, wherein the two anti-floating pieces are each in an arc shape and are arranged above the top sealing segment along the vertical central axis of the corresponding segment ring unit in a bilateral symmetry mode, the inner surfaces of the two anti-floating pieces face the corresponding top sealing segment, and the two anti-floating pieces are connected with the corresponding top sealing segment through one or more supporting screws, wherein the supporting screws and the corresponding top sealing segment are in screwingfit, and the outer ends of the supporting screws are in supporting fit with the corresponding anti-floating pieces. The anti-floating pieces act on a tunnel initial lining, the constraint effect is generated, upward floating of the segments is effectively controlled, and easiness and effectiveness are achieved.