We have solved the radiative transfer problem using a Sobolev approximation with an escape probability method in case of the supersonic expansion of a stellar envelope to an ambient medium. The radiation from the expanding envelope turns out to produce a P-Cygni type profile. In order to investigate the morphology of the theoretical P-Cygni type profile, we have treated $V_infty,;V_{sto},;eta$ (parameters for the velocity field), it and E(parameter for collisional effect) as model parameters. We have investigated that the velocity field and the mass loss rate affect the shapes of the P-Cygni type profiles most effectively. The secondarily important factors are $V_infty,;V_{sto}$. The collisional effect tends to make the total flux increased but not so much in magnitude. We have infered some physical parameters of 68 Cyg, HD24912, and $xi$ persei such as $V_infty,;M$ from the model calculation, which shows a good agreenment with the observational results.