Abstract:Aiming at the velocity-pressure mixed boundary problems of Stokes flow in exterior circular region, based on the character of the function of complex variable, the natural boundary element theory and series expanded method，the Poisson integral formula and the natural integral equation were deduced. The subsection linearity element was utilized to discretize the differential problems of the natural integral equation, and then the velocity value on the pressure boundary was computed, the velocity-pressure mixed problem was transferred into velocity boundary value problem. The velocity distribution was calculated by the Poisson integral formulae. The results showed that the velocity distribution by the natural boundary element method was according to the CFD software; the dimensionality of the problem could be reduced by the natural boundary element method, and the matrices of this approach were symmetrical positive ones. When the boundary was a circle especially, the matrices would be circulant, accordingly, the calculating volume was decreased greatly.