Abstract: Aiming at the problem that Gauss projection in the line engineering project needs to be frequently strapped and has low precision when designing the plane construction drawing of the project, this paper proposes a large elliptical Gaussian projection of an elliptical line projecting from the ellipsoid elliptical line of the route for the new central meridian, and analyzes the parametric theoretical model of the elliptic ellipsoid. Firstly, it derives the meridian arc length formula by using the naturalized latitude instead of the geodetic latitude as a parameter. Secondly, according to the quadratic curve invariant theory, linear algebra, calculus and other knowledge, it deduces the model of solving the basic geometric parameters of the large ellipse ellipsoid with the plane equation coefficient as the parameter. Furthermore, a direct conversion model of the geodetic coordinates between the base ellipsoid and the large ellipse ellipsoid is deduced. Finally, based on some actual engineering data, the correctness and superiority of the theoretical model deduced in this paper are verified to be popularized in long-term projects.