Abstract: The fluid flow mechanism in porous media of EOR by the surfactant-polymer flooding in horizontal wells was investigated by measuring production performance, input pressure and saturation distribution with saturation measuring probes in a 3-D physical model of vertical heterogeneous reservoir. Results show that, in a vertical heterogeneous reservoir, with the resistance increasing and the pressure going up, the flow direction changed under the physical and chemical actions of adsorption, retention and emulsion of SP agents in the reservoir. The SP agents displaced the remaining oil that water flooding did not affect and clustered remaining oil in the plane direction. Under the action of horizontal well, gravity and positive rhythm “low permeability barrier”, the fluid mainly flew in high permeability regions, and then flew from high permeability layer to the middle, last to low permeability regions which enlarged sweeping volume. So, the surfactant-polymer flooding in horizontal well can greatly enhance the oil recovery.