When the propagating shock wave reaches at the exit portal of a tube, the impulsive wave discharges to surrounding area and the expansion wave occurs from an open-end of a tube in the condition of subsonic flow behind the shock wave. The problem related to the reflection of propagating shock wave at the open-end has become more important subject associated with pulse combus-tors, pressure exchangers and high-speed railway train/tunnel systems. For the case of shock Mach number Ms less than 1.34, the reflected expansion wave generated at the open-end propagates toward upstream of a tube against the direction of the incident shock wave. For the cases of reflection at an open-end with no-baffled tube, Rudinger suggested the empirical equation concerning the imaginary center of reflected expansion wave. In this paper, the improved empirical equation considering the influence of the diameter of a baffle plate at the open-end was proposed. The experiment study using the simple shock tube and the numerical calculatdon using the TVD method were carried out.