The behaviour of deflagration and detonation was studied,for the gaseous mixture of nitromethane and oxygen by means of pressure gaufe and photodetection techniques in an explosion shock tube. It was found that the deflagration (ordetonation) pressure and velocitv increased fluctuantlv with the increase of nitromethane content in the gaseous mixture,The humps formed here from are obviouslv different from the upside down“U”curve of general explosion mixtures. Furthermore,a strong detonation could occur on the end plate of the explosion tube after reflection of the wead deflagration wave in the ignited gaseous mixture.The detonation pressure on the end plate is about 45MPa.CHO,OH radical emission excited by detonation are 10 times greater than that excited by deflagration.