An improved uncoupled solver of non equilibrium flow was adopted to resolve the Euler reacting equations and a chemical H₂/air mixture reaction model with 9 species and 21 equations was employed to conduct the two-dimensional numerical simulation in detonation onset process of vertical hot jets. The convection term was dispersed with fifth-order WENO format and the time integration was iterated with second-order Runge-Kutta scheme. The flow fields in the detonation tube were analyzed in detail when hot jets were injected with different parameters (i.e.incident velocities, incident positions, incident widths and incident angles). And the general rule of the impact of hot jets parameters to the detonation initiation was summarized. Moreover, interaction between shocks and flame during the formation and propagation of “hot spots” was explained, especially the promotion of reflected shocks on the formation of “hot spots”. The investigation reveals that detonation always occurs from the “hot spots” in narrow unburned region which is confined by adjacent flame front and solid wall. Triple point structures emerge during the over-driven transition of “hot spots” to detonation. In order to achieve rapid detonation onset, the hot jets should be injected towards the side wall in high velocity and with a certain angle.