The invention discloses a segment connecting structure of a quasi rectangular shield tunnel and a construction method thereof. An entire circle of segments is formed through splicing a plurality of segment blocks. The method comprises the steps of arranging bolts used for connecting two adjacent segment blocks at the joint parts of a plurality of segment blocks, in positions of which the distances relative to the inner ring surface of the entire circle of segments are the same; and analyzing to obtain the internal force distribution condition of the entire circle of segments according to a finite element model, moving the bots at the joint part bearing sagging moment by a first distance in the direction near the inner ring surface of the entire circle of segments, and moving the bots at the joint part bearing hogging moment by a second distance in the direction away from the inner ring surface of the entire circle of segments. According to the method, the blots at the joint parts bearing sagging moment are closer to the inner edges of the segments, the blots at the joint parts bearing hogging moment are closer to the outer edges of the segments, and compared with the usual arrangement form that the positions of bolts at the sagging moment and hogging moment parts of shield tunnel segments are the same, the segment connecting structure has the advantages that the joint strength is improved, and the bearing capacity of the segments is improved.