To address the issue of orbit determination of space targets when using space-based single line-of-sight measurement information， a new observability index was established. The influence of higher-order perturbation terms on system observability was studied， and an orbit determination method was proposed using single line-of-sight measurement. Firstly， the system observability matrix was derived using the Lie derivative， the system observability index was obtained based on the locally weakly observable condition of the system， and the approximate formula for the observability of higher-order perturbation terms was derived. Secondly， under the assumption of a near-circular orbit， the relationship between the orbit parameters of the space target and observation platform and the observability index was established， providing a basis for the design of the observation platform orbit. Thirdly， an iterative least squares orbit determination algorithm was proposed， and the orbit determination error covariance matrix was derived. The numerical simulation results indicate that the observability of the system is seriously affected by the difference in orbital inclination between the space target and the observation platform， and the higher-order perturbation term improves the observability of the system by increasing the vector heterohedrality. The observation platform is kept away from its ascending node to ensure observability of the system. A large observability index results in high accuracy of orbit determination， and the standard deviation of position estimation error is greatly affected by the observability of the system and the observation duration.