The combustion characteristics of methane/moist air in micro tube combustors with different inner groove shapes and number were studied in the paper. It was shown that the combustion characteristic was basically the same in the smooth tube and the micro tubes with one specific shape inner groove. The appearance of multi-grooves made combustion temperature, fluid velocity and mass fraction of each cross-sectional components occur jumping change nearby the inner grooves. For all of the micro tubes, methane conversion rate decreased with the increasing of inlet velocity in each micro tube under the same equivalence ratio. Methane conversion rate in the micro tube within different number of micro-grooves was higher than that in the smooth tube. However, the conversion rate of methane in the micro tube combustor with triangular grooves, in turn, was higher than that of in the combustor within rectangular, trapezoidal grooves and the smooth tube. Finally, it was indicated that the micro tube combustor with a smaller shape factor was more favorable for the conversion of methane.