Abstract: Microscopic mechanism of the percolation of 2 phrases of gas and water in an etched porous net on a 2 dimensional glass board is investigated. Direct observation of horizontal pores shows that, driving of the 2 phrases of gas and water is quite different from imbibition. Although both of them are influenced by capillary force when gas and water flow slowly, the front of gas and water continuously flows and obviously skipps in the paths of big pores when they are driven. However, when they flow rapidly, an obvious phenomenon of viscous fingering could be found. The front of gas occurs as tree branches. The branching of it increases with the increasing velocity of gas and water. When water is imbibited slowly into pores along pore walls, it fills the small pore throats and fingers when driven by strong capillary force. It reaches every corner of the pore model along pore walls. The front of water propels evenly with the increasing velocity. Analysis of the micro-distribution of gas and water after experiment is helpful for improving oil and gas recovery efficiency.