The development and implement of space technology made the on-orbital service be possible. On account of kinds of constraints-affection, the maneuver time and time period should be chosen carefully for the servicing spacecraft (SSC) to provide on-orbital services. The concept of maneuver window was put forward and defined, also its constraints was analyzed. The calculation of the maneuver window between circular orbits under the energy limit was discussed with emphasis. The energy-save drifting maneuver window and the time-saving quick maneuver window were studied separately according to the emergency degree of the service mission. Simulation results indicate, under the condition of limited energy and unlimited time, that the co-orbit deployment has more maneuver opportunity than the other modes, and maneuver energy is the key constraint for maneuver window.