In this paper, a new initial orbit determination (IOD) method for space-based optical surveillance is proposed. The problem that orbit calculated result converges to observation platform itself orbit in process of IOD using optical observation measurements is discussed. The IOD problem using space-based angle-only measurements is transformed into the problem of solving nonlinear equations of slant-ranges based on semi-latus rectum equation and improved Gaussian equation. The analytical form of the nonlinear equations of slant-range is derived. A method to remove the singularities of nonlinear equations is proposed. The search range is narrowed by using orbital energy constraint. Finally, the properties of the roots of nonlinear conditional equations are verified and analyzed by using space-based observation data. The effectiveness of the method is verified by using the simulation observations from LEO (Low Earth Orbit) observation platform to LEO, MEO (Middle Earth Orbit), GEO (Geostationary Earth Orbit) and HEO (Highly Elliptical Orbit) targets.