SUMMARYA numerical study has been conducted for the understanding of #ame structure with the fuel composition of 40 per cent CO, 30 per cent H , 30 per cent N and an oxidizer composition of 79 per cent N and 21 per cent O in a counter#ow di!usion #ame. Numerical results are obtained for #ames over wide-ranged conditions of axial velocity gradients and ambient pressures. Main concern is specially given to e!ects of axial velocity gradient and ambient pressure on #ame structure.It is seen that the role of axial velocity gradient on combustion processes is globally opposite to that of ambient pressure, on the basis of the DamkoK hler number considering the balance of convection, di!usion, and chemical reaction. That is, chemical non-equilibrium e!ects become dominant with increasing axial velocity gradient, but are suppressed with increasing ambient pressure. Flame strength is globally weakened by the increase of axial velocity gradient but is augmented by the increase of ambient pressure. However, #ame extinction is described better on the basis of only chemical reaction and in this case axial velocity gradient and ambient pressure play a similar role conceptually such that the increase of axial velocity gradient and ambient pressure cause the #ame not to be extinguished and extend the extinction limit, respectively. It is suggested that a combustion process like #ame extinction is mainly in#uenced by the competition between the radical formation reaction and the third-body recombination reaction.