The temperature, ion current, overpressure and photoelectric signal of flame front at the same cross-section in square tube of laboratory simulation of tunnel are recorded by homemade thermocouple, homemade ion probe, pressure transducer and photoelectrical transducer at the same time. The parameters changes of flame front with the same gas concentration of 10.17% are compared with obstacles or without obstacles. The results show that, when the obstacles exists, the value of temperature is slightly lower, the temperature is from 1 303.7 ℃ down to 1 234.4 ℃ by close to ignition position and from 1 198.7 ℃ down to 902.5 ℃ away from ignition position. The value of ion current is slightly higher and the double peak values occur obviously in the signals of ion current, the peak value of ion current is from 1 46.25 nA up to 160 nA in the vicinity and from 432.5 nA up to 605 nA in the distance. The precursor compression wave in flame propagation tube is appeared ahead to further promote the gas explosion process in DDT. Therefore, roadway should minimize the presence of obstacles.