Conduct water flooding experiments on saturated rock cores in a confined water state, and combine nuclear magnetic resonance online displacement imaging with T2 spectra and micro CT scans to compare the water flooding patterns of matrix cores, fractured cores, and intermittent water flooding of fractured cores. Clarify the contribution of different scale pore throats to oil displacement efficiency and explore fluid flow characteristics in complex fracture network systems. Research has shown that the average oil displacement efficiency of matrix core is 36.32%, and water flooding efficiency in pores larger than 0.5 μ m can reach 33.46%–46.66%. However, in pores smaller than 0.5 μ m, the oil displacement efficiency is less than 30%. The average oil displacement efficiency of fractured rock cores is 29.78%, which is 6.54% lower than that of non fractured rock cores. The oil displacement efficiency of crude oil in pores with a scale greater than 1 μ m can reach 100%, while in pores with a scale smaller than 0.5 μ m, the oil displacement efficiency is only 1.02%–24.51%. The displacement mainly uses microcracks and the original oil in the matrix pores connected to microcracks. Water flooding experiments have shown that water flooding mainly utilizes fractures and a portion of crude oil in large pores, while it has low utilization efficiency of crude oil in small pores. Intermittent oil recovery utilizes the combined effects of water displacement and oil-water conversion in fractures, resulting in a further increase of 8.76% in oil displacement efficiency compared to conventional water flooding.