The kinetic effects of CO2 and H2O dilution on the laminar flame speed of acetylene at elevated pressure has been investigated experimentally using outwardly propagating spherical flames from 1 - 20 atm. A high pressure kinetic model is assembled by including pressure dependent elementary reaction rates determined by recent theoretical calculations and experimental measurements. It is found that, unlike other hydrocarbons, the kinetic inhibition caused by CO2 dilution on acetylene flame speeds via CO2+H=CO+OH is reduced at both fuel rich and lean conditions due to the existence of direct CO2 formation pathways (HCCO+O2 and CH2+O2) in acetylene oxidation. On the other hand, the inhibiting kinetic effects of water dilution on acetylene flame speed are promoted because the shifting equilibrium of the H2 O+O=OH+OH reaction inhibits production of O radicals needed for the O+C2 H2=HCCO+H chain propagation reaction. Detailed analysis on the combustion chemistry of acetylene reveals that C2 H2+O, HCCO+O2, HCO+O2, CH3+HO2, H+C2 H3, CO+OH, CH2(S)+C2 H2, and HCO decomposition are among the most important reactions for predicting the laminar flame speed, especially at high pressures. The results show that the new high pressure model (HP-Mech) improved prediction of flame speeds of acetylene with CO2 and H2O dilution.