Flow separation phenomenon exists in the nozzle of the high altitude rocket engine when it was tested at the grownd.Numerical simulation was carried out for the flow separation in overexpanded rocket nozzle using Beam Warming approximate factorization method to solve thin layer N S equations.The location of Separation region and distribution of wall pressure in the nozzle were predicted.These will be the references of high altitude rocket engine test and provided basis for studying the influence factor...