Rotating detonation engines have attracted considerable attentions in recent years. In this study, the experiments of initiating rotating detonation waves were performed on a H-2/air rotating detonation wave with the variable air-inlet slot. The results showed that the stability of detonation-wave pressure and velocity both initially increased and then decreased with the increase of slot width, and it could improve the stability of detonation wave velocity via increasing the equivalence ratio. The intensity of reflected wave was strong for the tests of d = 0.5 mm, which leaded to the advance ignition of fresh mixture and a velocity deficit reaching up to 20%. The strong interaction between air plenum and combustor and bad mixing effect may be the reasons of forming unstable detonation wave for the tests of large-scale slots. The air-inlet slot of d = 1 mm, which got a best experiment results relative to other tests, had a wide equivalence-ratio scope to produce stable detonation wave. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.