Abstract: By analyzing the segment erection process and the force applied on the segment, a finite-element method was adopted to study the variation law of the opening angles of longitudinal joints under different erection ovalities and different positions of the key segments. Additionally, the maximum internal and external openings at the sealing gasket were calculated for when the key segment is at the most unfavorable position. Research results indicate that: there is a linear relationship between the erection ovality and the segment opening angle, the position of the key segment affects the magnitude of the opening angle under the same erection ovality, the opening angle is at a maximum when the key segment is positioned at an angle of ±32.7276°, and the maximum opening at the sealing gasket is 5.1mm under the ovality of ±5‰D at this position.