Combustion characteristics of the transient hydrogen jet were investigated by the experiments. Bulk quenching was found to occur in the periphery of the jet due to the low fuel concentration. Then the flame propagation into the lean region in the jet was investigated. Hydrogen was injected into the lean hydrogen-air mixture charge around the lower flammability limit of the premixed mixture. The flame generated in the fuel jet propagated into the lean mixture charge region as if it had as “inertia”. Then it was quenched in the premixed mixture charge. The flame seems to be supported by the burned region from its back until the decay of this support. In order to investigate this “flame inertia”, the interactions between the rich flame and the lean mixture were investigated by the numerical simulations of counterflow premixed flame. Reaction rate of the fuel in the lean mixture depended on the opposing gas temperature.