Non-premixed hydrogen micro-jet flames in co-flow airs were studied by numerical computations with a detailed chemical reaction mechanism. The results of numerical computations agreed reasonably well with the counterparts of the experiments. The results showed that the computed maximum flame temperature decreased with decreasing fuel injection velocity for a fixed micro tube. When the fuel injection velocity was close to the minimum flow velocity sustaining a flame

the computed maximum flame temperature decreased sharply with decreasing fuel velocity. The wall materials had an influence on flame structures at a low fuel velocity. The lower the thermal conductivity of materials

the higher the wall temperature near the nozzle exit. The maximum flame temperature on the axis was relative higher. However

the effect of thermal conductivity on the quenching velocity of flame was not remarkable.