The capillary evaporation process with stable liquid film along the cell wall is investigated by evaporating under constant temperature. The experimental results show that the liquid/vapor interface coincides with viscous finger, which is independent of the state of liquid film and evaporating rate. During the evaporation process, four stages are found: sharp falling rate stage, constant rate stage, linear falling rate stage and boundary effect stage, which are corresponding to different kinds of liquid film states. The evaporating takes place mainly at the tip of the liquid film region, and the stable liquid film transports the liquid from the liquid region to the capillary tube orifice.