A co-flow jet (CFJ), an active flow control method combining blowing and suction control, can effectively suppress the stall of airfoils. However, the streamwise jet channel along the upper surface of a conventional CFJ airfoil reduces the thickness and camber of the baseline, degrading the aerodynamic performance when the jet is inactive. The conformal slot CFJ airfoil was proposed to address this problem, but the design method is still absent. This paper proposed a general design method based on parameters including the slot angle, transition shape and distance of the injection and suction slot. The mechanism of the best parameter was analyzed. The designed conformal slot CFJ airfoil was checked under different jet intensities, and the turbine power curve was predicted when substituting CFJ airfoils for the baseline. Compared with the conventional CFJ airfoil, the designed conformal slot CFJ airfoil has three advantages: eliminating the performance loss when the jet is off, saving jet energy when suppressing the flow separation, and improving the power generation of wind turbines at low wind speeds.