Abstract: In order to meet the requirement that the projection length deformation value of the high-speed railway line control network is not more than 10 mm／km, it is necessary to divide the line into multiple sections and establish their respective normal section meridian ellipses. For the adjacent connection problem of the ellipsoid, the method of the intersection point with same normal is proposed, the consistency of the intersection points after the ellipsoid transformation is realized, and the seamless connection problem of the lines is solved, thereby greatly enhancing the applicability of the normal section meridian ellipsoid theory in the bending property, complexity and length of the engineering line.