Abstract: Foam flooding is an effective method to retard gas chan- neling,fingering and gravity override in the process of gas flooding.As foam flooding is widely used in EOR process, summarized are three mechanisms on foam generation in por- ous media,including snap-off,liquid--film division and liquid-film remains.Effects of:the fluctuation of capillary pressure,the geometry of pore throat,the rate of flow,the topology of pore network,the property of interface and crude oil on the formation of foam are discussed.It is point- ed out that effective experimental method is still needed to study the generation mechanism of foam under the condition of stratum.