Abstract: To meet the technical requirements of well anti-collision evaluation, this study creates the methods of distance calculation and anti-collision evaluation between the reference well and offset wells, and also performs case analysis. By establishing the wellhead coordinate systems and their transformation relation based on the earth ellipsoid, the positioning error caused by the deformation of map projection and no consideration of the curvature of ellipsoid surface were eliminated to achieve the precise positioning of offset wells. According to the theory of extreme value of function and differential geometry, the methods of calculating the closest approach distance and the normal-plane distance based on the derivative function are presented, which not only solves the problem that the existing methods may miss the risk point of well collision, but also can apply to various wellbore trajectory models. Based on the direction of scanning vector of well anti-collision and the posture of error ellipsoid of wellbore trajectory, this paper proposes an analytical method to solve the intersection position of scanning vector and error ellipsoid, which lays a foundation for the accurate calculation of separation factor, and the research results provide a complete set of evaluation methods for well anti-collision evaluation.