In order to determinate the orbit of space objects, an orbit-determination method with particle swarm optimization (PSO) using space-based optical short-arc observation in admissible region was proposed. The concepts of the attributes, the admissible region and the construction of optimization-function were introduced. A method with PSO for searching best key to optimization-function was proposed to avoid the problem of various keys, local optimizations and mass calculations. An orbit-determination course was simulated with 3rd part software to validate the correctness of the proposed orbit-determination method. Simulation results indicate the proposed method with PSO reaches more precise orbit without various keys and mass calculations, the performance of proposed method is close to Crame-rao low bound.