Detonation performances of methane/hydrogen/oxygen (CH4/H-2/O-2) mixtures were investigated experimentally in a 3000 mm long tube with an inner diameter of 30 mm at different initial pressures p(0) (ranging from 10 kPa to 50.5 kPa). Mixtures with different proportions of H-2 in the total fuel alpha (0%, 14.29% and 25%) and different equivalence ratios Phi (0.8, 1.0 and 1.2) were tested. Signals of flame front and pressure were obtained by ion probes and high frequency pressure transducers, respectively. Results showed that with the increase of p(0), alpha and Phi, the average velocity of steady detonation V-aue increased. For mixtures with the given alpha, when Phi increased by 0.2, V-aue increased by 100 m/s. In the present study, velocity deficits were found to be within 5%, and when p(0) was higher than Detonation 20 kPa, the velocity deficits were within 2%. The average peak pressure of steady detonation p(ave) was close to the von Neumann pressure p(vN). Both the increase of p(0) and Phi led to Velocity deficit the increase of the p(ave). But the addition of H-2 led to the decrease of p(ave), and p(ave) decreased Pressure with the increased of alpha. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.