The emission spectrum of the transition from deflagration to detonation for the mixture of hydrogen and oxygen are successfully measured with polaroid high speed film. The evolution of OH radical (0.3064 μm, 0.3428 μm) for this transition is also observed by photoelectrical technique. The results show that the OH radical emission for the transition from the deflagration to the detonation gradually increases, when the detonation is formed, OH radical emission obviousely increase. OH (0,0) radical emission is earlier than O2(0,14). These data indicate that the energy of O2 in the chain reaction is lower, and O2 are excited via O2 interaction with free-atoms or redicals acquired more energy.