Abstract: One dimension pulse detonation waves are simulated with three step chainbranching reaction mechanism, and the propagation mechanism is discussed from the viewpoint of the energy release. Numerical results show both the average energy release and the ratio of the internal and kinetic energy are invariant although the detonation waves show different oscillation characteristics. The phase difference of the shock and postshock combustion is used to explain the instability derived from the shock, and the unstable detonation has the larger phase difference. The phase difference also provides the physical understanding of the doublemodel pulse detonation waves, which overwhelms the large oscillation length and phase difference to avoid the detonation quench.