In this work, laminar flame speeds of CH4/CO/air mixtures were measured at the unburnt temperature of 353 K and pressures from 1 to 10 atm in a high-pressure constant-volume cylindrical combustion vessel. Effects of pressure, equivalence ratio and CO content in CH4/CO mixtures on laminar flame speeds were investigated. A kinetic model for CH4/CO combustion was developed based on recent progress in elementary reactions and validated against previous and present experimental targets. It is found that both the thermal effect originating from different adiabatic flame temperatures and chemical effect originating from differences in the radical pool play important roles in the variation of laminar flame speed. The separate contribution of each effect varies at different pressures, equivalence ratios and CO contents. Besides, the transition from CH4-related chemistry to CO-related chemistry can be monitored by the increasing concentration of 0 atom in the radical pool under all the investigated conditions. Based on the modeling analysis, R18 (CH3 + CH3 (+M)=C2H6 (+M)), R19 (HCO (+M) = H + CO (+M)), R6 (CH4 (+M) = CH3 + H (+M)) and R7 (CH4 + H = CH3 + H-2) have major contributions to the transition chemistry, especially under the rich conditions. Compared with the atmospheric pressure conditions, R20 (CO + O (+M)=CO2 (+M)) and R22 (H + O-2 (+M)=HO2 (+M)) are enhanced at high pressures, which leads to the decrease of 0 atom in the radical pool at high pressures. (C) 2019 The Combustion Institute. Published by Elsevier Inc. All rights reserved.