Flame modes and liftoff hysteresis of the methane/oxygen inverse diffusion flame (IDF) are experimentally studied in still air. The effects of gas velocity on flame mode and liftoff hysteresis are investigated by changing the gas flow rate, and the influences of gas velocity on OH* distribution in different modes of flame are investigated using an ultraviolet camera. The results show that methane velocity, oxygen velocity and history of the flame mode are the key factors in determining the flame mode. Flame mode regimes are identified according to the three factors. The OH* profile along the axis of the nozzle in the IDF indicates that the reaction zone is narrow in fuel rich condition and broad in fuel lean condition. The hysteresis characteristics of the IDF are significantly influenced by the coaxial methane velocity. With the increase of coaxial methane velocity, the liftoff velocity and attachment velocity of the IDF decrease linearly, while the transition velocity increases linearly from partly premixed flame to IDF.