Abstract: The numerical simulations based on former physical experiments showed that the efficiency of secondary oil-gas migration was controlled by oil-gas migration mode.The oil-gas migration mode can be divided into three types of piston mode,fingering mode and string mode.In all of the modes,the efficiency of the piston mode is the lowest,and the efficiency of the string mode is the highest.The characteristics of three migration modes are different.The oil migration efficiency of piston mode was unchanged with physical conditions.The scale of the migration space had some effects on the oil migration efficiency of the fingering mode.The efficiency of the string mode had the most complicated affecting factors.The physical conditions resulting in the change of the buoyancy force or capillary force had some affection on the oil migration efficiency of the string mode.