On the basis of the detailed analysis of the basic detection evaluation parameters, point target evaluation parameters and area target evaluation parameters, this paper effectively resolves the limitations of the day and night backgrounds by the optical spectral segment selecting according to the optical properties of the low speed target in the near space, and designs a near space low speed target detectability evaluation system and optimization scheme based on optical method. Moreover, in consideration of the spectral constraint condition, the position constraint condition, the detection ability and the evaluation parameters of the optical detector in detailed through different equivalent effect curve surfaces of single and multiple detectors by numerical, the simulation result indicates that when the target is inside the equivalent curve surface, the detecting effect is better than that of the expectation and can meet the needs of the detection requirements, on the contrary, the detection effect is worse than that of the expectation, and cannot meet the needs of the detection requirements, unless the detection scheme is modified. The results show that the near space low target detectable evaluation system is effective based on the optical method.