Abstract: Gaseous detonation diffraction in abruptly expanded tube and gradually expanded tubes was numerically investigated at different filling and expanding angles.Detonation tube diameter and critical tube diameter are vital to the successful diffraction.Interaction of the wall reflected shock and the detonation wave produces a high temperature and high pressure region,helping to reduce the detonation inducement time and the distance between transverse waves.The small expanding angle can generate strong reflected shock.If the reflected shock is strong enough,it will separate the detonation wave into 3 parts generating high temperature,high pressure regions at the cut-off points,providing a support to detonation diffraction.