The invention relates to a segment structure applicable to quasi-rectangular shield tunnels. The segment structure with the cross section being quasi-rectangular comprises an arch bottom arc section located at the arch bottom of the cross section, an arch crown arc section located at the arch crown of the cross section and two arch haunch arc sections located at the arch haunch positions on two sides of the cross section; the arch haunch arc sections are equal in radius which is smaller than the radius of the arch bottom arc section and the radius of the arch crown arc section; the arch bottom arc section is connected with both the arch haunch arc sections in smooth tangency, and the arch crown arc section is connected with both the arch haunch arc sections in smooth tangency. The segment structure has good arching effect, bending moment and eccentricity upon lining segments are reduced favorably, reinforcement consumption and lining thickness needed are reduced, and corresponding soil excavation volume and concrete consumption are less. In addition, shield equipment can cut soil mass on the whole section beneficially, and impact on surroundings is smaller.