Abstract: Partially-filled open flow in circular-shaped pipe behaves unique hydrodynamic characteristics due to the special cross-section geometry. To investigate the peculiar characteristics caused by two-sides double-curvatures, a three-dimensional numerical model, based upon RNG k-ε turbulence model and FAVOR (Fractional Area/Volume Obstacle Representation) is established, and further verified using physical experiment results. The presented numerical model is then applied to simulate partially-filled flows with different combinations of slopes and filling degrees, in order to explore the velocity distribution, wall shear stress and Reynolds shear stress. The results indicate that velocity-distribution profiles along the different vertical lines generally follow a parabolic function, and a regression expression is proposed. A unified formula for the wall shear stress along wetted perimeter with different filling degrees is presented. The results also show that the Reynolds shear stresses linearly distribute along vertical lines. The larger the filling degree and distance from mid-perpendicular are, the smaller variation gradient of the stresses is. When filling degree is greater than 0.5, due to the influences of the secondary flow, the negative Reynolds shear stress appear along the mid-perpendicular.