The multiphase flow driven by the capillary pressure in the anode flow field of a micro direct methanol fuel cell (μDMFC) is modeled based on the porous media theory. The electrochemical reaction at the anode is taken into account in this model. Parametric studies of the channel size and the power density are carried out to assess the effects on the transport characteristics of the multiphase flow driven by the capillary pressure in micro channels. In addition, the effects of the channel size on the cell performance are discussed. The results show that the liquid saturation in micro channels increases with the increase of the width and height of the channel, but decreases with the increase of the channel pitch and the power density. The cell performance is improved with the increase of the channel width and height. A larger channel pitch and length lead to a lower power density.