Abstract: The process of super-knock combustion under a high compression ratio engine was conducted to analyze the role of pressure on end-gas auto-ignition during deflagration-to-detonation transformation（DDT）,and the way of self-sustainment during developing detonation. Analysis result shows that pressure is the main connection between deflagration and spontaneous spots as well as the trigger of detonation. Furthermore,different from the piston compression,this compression of pressure is directional with experiencing two compression waves in a short period of time,which results in the onset of auto-ignition always near cylinder wall. In addition,maintaining the detonation requires the new spontaneous ignition in front of the pressure wave to accelerate pressure wave speed.These kind of new spontaneous ignition points have two different state,in which the energy release rate decreases and/or increases compared with the pressure wave speed. The whole process is as follows:spontaneous ignition develops into spontaneous ignition state 1 caused by pressure wave triggering,and the pressure wave slowly increases to initiate spontaneous ignition state 2. In state 1,the energy release velocity decreases relative to the pressure wave velocity,and in state 2,the energy release velocity increases relative to the pressure wave velocity.