Based on the first-order Arrhenius kinetics of chemical reaction and hydrodynamics, we proposed a mechanism to interpret the physical process of detonation onset. In the proposed mechanism, all the movements of chemical mixture are described by the characteristic waves of hyperbolic system. Each wave in different manner contributes to the transition from deflagration to detonation. The triggered detonation is the result of interaction of the multiple waves, more accurately, is a direct result of the re-ignition in the gaseous explosive in the unreacted zone by the reaction-released energy that is transferred in the form of the characteristic wave. This mechanism provides a complete and theoretic explanation to "explosion in the explosion" observed in experiments. It associated with the traditional ignition theory may be used to build up the criterion for deflagration-to-detonation transition (DDT). The mechanism is further verified by our numerical solutions to the mathematic model. (C) 2012 Published by Elsevier Inc. on behalf of The Combustion Institute.