The thick oil layers of Lamadian Oilfield in Daqing are mainly characterized by multiple intervals and multiple rhythms. Deeply understanding the channeling law is crucial for further tapping the potential of the remaining oil. Therefore，intralayer heterogeneous cores were used to study the internal channeling law of intra-layer heterogeneous reservoirs experimentally. The results show that in the stage of water flooding with an injection volume of 0-0.4 PV，the diversion rate at the injection end is slightly lower than that at the production end in the high-permeability layer，which is opposite to those observed in the medium-and low-permeability layers；in the stage from water flooding with an injection volume of 0.4 PV to the end of water flooding，the diversion rate at the production end of the high-permeability layer greatly increases，while the diversion rate in the medium-permeability layer significantly reduces and that in the low-permeability layer slightly decreases. With the increase in the core permeability ratio，the channeling degree between the sublayers at the production end and the injection end decreases，and the same goes with the interlayer interference. As water flooding continues，the channeling degree of interlayer first decreases and then increases. As the injection rate goes up，the diversion rate difference between the production end and the injection end of the high-permeability layer increases，hence the channeling degree rising. Increasing the injection rates of water wells can achieve the purpose of raising the injection pressure. Nevertheless，because the increase in fluid absorption in the high-permeability layer is much greater than those in the mediumand low-permeability layers，besides the influence of channeling inside the reservoir，the effect of expanding the swept volume is not distinct. Moreover，increasing the injection rates of water wells also puts forward higher requirements on the capabilities of equipment at the injection end and the production end and that on the surface. Therefore，increasing the flow resistance of the high-permeability layer is the effective technical way of increasing the injection pressure.