The existence of dominant flowing channels after polymer flooding leads to low sweep efficiency and then further results of low recovery factor. So it is urgent to solve the problem of how to describe the distribution and seepage characteristics of dominant flowing channels effectively in the process of Daqing oilfield development after polymer flooding. According to the data of pressure cored wells and logging, the definition and distribution features of dominant flowing channels are determined after polymer flooding, then their seepage characteristics is studied by physical modeling and numerical modeling, etc. The thickness percentage of dominant flowing channels is increased by 9.3% than that before polymer flooding. They are mainly concentrated in the thick oil layers vertically and distribute in a wide range horizontally. The thickness percentage of dominant flowing channels is about 20%, but the flux ratio of them can reach up to more than 50% leading to serious invalid circulation. The study of dominant flowing channels distribution and seepage characteristics after polymer flooding provides a foundation for following plugging scenario design, which can further enhance oil recovery after polymer flooding.