This article addresses the effect of hot jet condition on detonation initiation characteristics. Hot jets with different conditions were generated by changing the length of the pre-detonator. The change relationship between the detonation initiation characteristics and the jet condition was investigated by numerical simulation and experiment. The simulation results showed that a detonation wave could not be initiated by the low velocity jet (subsonic), but could be initiated by the high velocity jet (the supersonic jet and detonation jet) under the current simulation conditions. Meanwhile, the ignition and detonation initiation time, hot jet detonation initiation time, and detonation initiation distance in the main-detonation tube decreased as the velocity of the hot jet increased due to the increased pre-detonator length. The multi-cycle detonation experiments of pulse detonation engines (PDEs) were conducted to validate the simulation results by using a pre-detonator with two different lengths. The experimental results indicated that the ignition and detonation initiation time and hot jet detonation initiation time both decreased with increased jet velocity resulting from the increased length of the pre-detonator, which was basically consistent with the simulation results.