Abstract: With the exploration of the adhesive work between fluid and pipe-wall, the drag reduction mechanism for the pope flow of Casson fluid is brought to light. It is belived that wall slip is the nature of drag reduction when fluid flows in pipe flow. Further more, the drag reduction rate in pipe flow is presented, and the relevant factors are also analyzed systematically. Some pratical measure are provided to realizing dragreduction of pipe flow of Casson fluid.