This paper numerically studies the performance of 3D Co-flow Jet (CFJ) control surfaces to achieve ultra-high control authority with zero-net-mass-flux flow control at low energy expenditure. The effects of CFJ moment coefficient (Cµ ), sideslip angle (β) and deflection angle (δ) are investigated. The 3D swept vertical tail tested by Selee et al is used as the baseline for comparison. Numerical study is conducted with unsteady simulation due to the highly unsteady flow of the tip vortex induced by the low aspect ratio swept control surface and the vortex generated by the gap between the control surface root and the wall. The high fidelity in-house CFD code FASIP with the Improved Delayed Detached Eddy Simulation (IDDES) turbulence modeling is utilized. The predicted lift and drag coefficients achieve a good agreement with experiment for the baseline control surface with the maximum discrepancy less than 3.8%. The numerical simulation indicates that applying co-flow jet on control surface is very effective and energy efficient. A small Cµ of 0.025 generates a 28% CL increment at 0 sideslip angle with a higher corrected aerodynamic efficiency ((CL /CD )c ) than the baseline case. With the Cµ of 0.26, the CL is increased by 99.25% at 0 sideslip angle and the CD drops 52% due to removal of the flow separation and suppression of the tip and root vortices by the co-flow jet. A phenomenon not observed in a regular CFJ wing without flap is that the second pressure suction peak at the flap shoulder is higher than the leading edge suction peak. It is attributed to the attached flow experiencing a rapid turning due to the flap deflection, which creates a local acceleration that significantly reduces the pressure. The CFJ control surface also has much higher stall margin than the baseline control surface. With Cµ =0.26, the CFJ control surface stalls at the sideslip angle of 27.5◦, which is 2.2 times higher than that of the baseline control surface of 12.5◦ and a very high CL of 2.84 is also achieved. Furthermore, with Cµ =0.26 and zero sideslip angle, a very high CL of 1.88 and 2.12 is achieved at δ=40◦ and 50◦, which is 2.3 and 2.5 times of the baseline cases respectively.