Abstract: A researching method for flow separating of solid launch vehicle orbit maneuver motor nozzle is proposed in this paper. The theoretical calculation is carried out for studying the influence of flow separating on the nozzle performance. The numerical simulation analysis is done to obtain the flow separating location, thrust coefficient, wall-surface static pressure, coefficient of convective heat transfer and distribution of temperature field. Results indicate that the ground thrust coefficient is 73.3% of the vacuum thrust coefficient for the engine energy conversion efficiency reduced. Parameter jumping caused by flow separation is harmful to nozzle working. Flow separating research based on using the ground test indicating altitude performance of nozzle gives some suggestion of nozzle thermal protection design for reference.