Abstract: Based on a Ruby-laser schlieren system, the flow-field of detonation diffraction in a bifurcated tube has been experimentally studied. By employing the ruby laser and a bandpass filter of 15 nm FWHM, the combustion luminescence was successfully removed in experiments. By setting proper predetermined time delay of the synchronization unit, schlieren image series at the different time were obtained. The results show that the transverse waves, leading shock and reaction zone can be clearly observed in the consecutive images. Influenced by the rarefaction waves from the left sharp corner, the leading shock was disturbed and separated from the reaction zone. Therefore, the detonation wave was degenerated into a deflagration wave. The decoupled leading shock and the winkled reaction front can also be identified in the schlieren images. Re-initiation was induced by the leading shock reflection on the right wall in the vertical branch. Mach reflections of the disturbed detonation waves occur in both the vertical and the horizontal branches. With increasing the initial pressure of the premixed mixture, it was earlier for the disturbed detonation waves to be recovered to self-sustaining detonation waves in the vertical and horizontal branches.