Abstract: According to the principle of fluid mechanics, the law of laminar, helical flow of power-law fluid in eccentric annuli is studied extensively in this paper. The apparent viscosity, velocities distribution of laminar helical flow of power-law fluid are discussed and calculating methods of flow rate and pressure loss are presented. The factors influencing flow are also analysed. On the basis of theoretical studies some new results of the present paper are compared with the theories of the helical flow of the power-law fluid in concentric annuli. The test verified that theoretical formulas in this article are proper and general. They can be used for calculating hydraulic parameters in drilling engineering.