As the examples of smoke spread in a corridor, the burn rooms are generally connected through a corridor to environment and a lobby. The wave amplitudes of the velocity of transient jet waves are very important in fire protection systems. The objectives of this study are to estimate mathematically the parameters of the transient jet wave velocities flowing through the unconfined ceiling of the corridor and to derive various related equations with the parameters. The parameters vary according to the wave induced velocity, the natural frequency, the wave number and the mean flow velocity. The transient ceiling jet waves are analyzed by FDS software developed by the National Institute of Standards and Technology, USA. The analyzed results of the smoke layer temperature are compared with the experimental results performed by Jones et al.. The relation of the mean velocity, the heat release rates and the door width is expressed by the relation of the wave induced velocity, the heat release rates and the door width is expressed by .