Abstract: The performance and lifetime of direct methanol fuel cell (DMFC) are great influenced by whether the CO2 produced from the catalyst layer can vent from the diffusion layer and the anode channel. Thus，the understanding for the mechanism of bubble behavior is essential for DMFC optimization. In the present study，the bubble behavior from the anode diffusion layer into the anode channel in DMFC was simplified as the process of bubble formation and detachment from cross-orifice in steady liquid flow，which was experimentally investigated by using a visual system. Effects of the gas/liquid flow flux and the buoyancy on bubble formation and detachment were investigated. Results showed that the bubble formation is dependent on the gas pressure and the capillary pressure produced by surface tension. Compared with the bubble gestating process，bubble formation and detachment are much quicker. With the gas flow flux increase，the time interval of bubble formation decreases，the bubble coalescence site moves forward，the detaching time decreases first and then increases. With the liquid flow flux increase，slug flow evolves to bubbly flow gradually，the detaching time decreases quickly first and then becomes constant. The buoyancy has a strong impact on the bubble formation in down direction. It is much more difficult for bubble to form and detach from the orifice in down direction，which contributes to the buoyancy effect.