Freckles are presently one of the main casting defects in the single crystal(SC)components made of superalloys. In the present work,a series of SC components with complex geometry, including turbine blades, were directionally solidified. It was found that the casting shape has more significant influence on the freckle formation than the local thermal condition. On the transverse sections of the components with curved contour, freckles were exclusively found on the outward curving surfaces having positive curvature, because the surface effect zones of the neighboring sides are overlapped, providing more favorable convection condition. In comparision, the surfaces with negative curvature remained freckle free, because the surface effect of the neighboring sides is divergent from each other. In the longitudinal direction, the freckle formation can be promoted by contracting contour and suppressed by expanding one, respectively.