The effects of different diluents and dilution ratios on laminar burning velocities of hydrogen/oxygen/diluents mixtures were studied at elevated pressures and temperatures with a constant volume combustion chamber and a high-speed schlieren system. Both experimental and numerical laminar burning velocities of hydrogen/oxygen/diluents mixture were obtained at equivalence ratios of 0.6-4.0

initial pressures of 0.1-0.5 MPa

and dilution ratios of 4-8. The results showed that the laminar burning velocity varied non-monotonically with the increase of the initial pressures and equivalence ratios among 1.0-3.0，and the laminar burning velocity deceased with the increase of initial pressure when the equivalence ratio was less than 1.0 or more than 3.0. Through sensitivity analysis of elemental reaction

three-body reaction(R15) was found to restrain reaction in nitrogen diluted mixture

and promote reaction in both argon and helium diluted mixtures

mainly due to different thermal physics properties of different diluents.When the equivalence ratios were within the ranges of 1.0-3.0

the non-monotonic change of laminar burning velocities with the increase of initial pressures was mainly due to the competition between chain-branching reaction R1 and chain-terminating reaction R15.