Abstract: An experimental investigation on the high-speed deflagration in the acetylene-oxygen mixture was carried out in a smooth straight tube. The deflagration was generated by putting a perforated plate in the way of a self-sustained detonation wave and interrupting it. Streak schlieren photos were taken to illustrate the averaged structure of the initially transmitted deflagrations near the plate, and pressure transducers were used to trace the further development of the wave front. The high-speed deflagration wave was found to be a complex of precursor shock and flame. With the increase of the initial pressure, it varies from a laminar structure to a turbulent one, and the onset of the latter seems corresponding to the smaller or comparable cellular width of incident detonation to the disturbance scale of perforated plate. This study reveals that deflagrations with laminar structure can not stand the attenuation of background rarefaction and keeps on slowing down, whereas the turbulent one is capable of running up and transiting to a detonation wave. There is an unstable critical case between the mentioned two situations, where the deflagration can propagate for a relatively long distance at a 0.5~0.6 times CJ detonation speed. This critical case matches the constant-volume combustion solution of the Rankine-Hugoniont relations across dual discontinuities.