Abstract: For reservoirs in land oilfield with strong heterogeneity, long-term waterfloodingcan easily create preferential water flow passage, causing ineffective water circulation, reducing the sweep coefficient, and severely impacting the development effectiveness. Take Fuyu X17-19 Block as an example, based on core and thin slice observation under microscope, the preferential water flow passage within this block is divided into three categories: seepage, pipe flow and seam flow. The three flow passages connect with each other in space and form a complex channeling network system with multiple combination patterns, dominated by ’water well – natural fracture – highly seeping zone – fractures – oil well’. The profile, the plane distribution and the dominant factors of the preferential water flow passage were analyzed based on the data of core, logging and production performance, and the reasonableness of the results were identified based on sedimentary micro-facies and high permeability area, and it was thought that there existed preferential water flow passage in direction of wells X17-019.4 and X17-19.1 in six small layers of No.Ⅱ. sand group. The purpose of treatment by breaking the present water flow network is achieved by deep flooding or well pattern adjustment based on the types and intensity of preferential water flow passage.