Abstract: In order to understand the process of shock movement,soot records were obtained by arranging a window of 60 mm×1 380 mm laterally onto a square donation tube.A series of single detonation experiments were conducted to study the performance of C₂H₂/air and H₂/air mixtures in square detonation tube.The pressure transducers and ion-probes were utilized to measure the pressure and velocity in the tube,respectively.The results indicate that : ① Soot records is one of direct and effective means;② Overdriven detonation appears only once and several blasts appear in DDT(Deflagration to detonation transition);③ The dimension of acetylene is less than that of hydrogen under the same initial condition.