In this study, combustion characteristics and flame structures of low temperature flames of lean hydrogen mixtures are investigated by chemical kinetics computations. Several mixtures having nearly the same laminar burning velocities of 15, 25 and 35cm/s are prepared by adding nitrogen to hydrogen-oxgen mixtures with equivalence ratios ranging from 0.3 to 0.9. Initial pressures are varied from 1 to 4 atm at the initial temperature of 298K. As a result, it is clarified that low temperature reactions (R05:H+O2+M⇔HO2+M, R06:H+HO2⇒OH+OH, R04:H2+OH⇔H2O+H) are dominative in these flames regardless of the initial pressures, however, there are differences in flame structures and combustion characteristics depending on the equivalence ratio.