Abstract: In order to investigate the characteristic of deflagration to detonation transition(DDT) in close end with 5 kinds of block ratios,a series of single detonation experiments were conducted to study the performance of acetylene-air mixtures in square detonation tube of 60 mm×60 mm×2 000 mm.The ion-probes and pressure transducers were utilized to get the velocity and pressure in the tube,respectively.The results indicate:(1) Position of DDT moves back with the accretion of block ratio in close end;(2) The block degree does not affect essential characteristic of DDT.