Numerical study is carried out to investigate flapped delta wing low speed performance with coflow jet (CFJ) flow control at Mach number of 0.1. Two delta wings formed by thin supersonic airfoils with aspect ratio of 2 and 0.67 and sweep angle of 53◦ and 63.5◦ are studied, but only the detailed results for the wing with aspect ratio of 2 are presented. The simulation is validated very well with the experiment. The flap has a constant chord along span and is 24% of the root chord. CFJ is applied in two ways: one on top of the main front part of the delta wing and the other is on the deflected flap. Both are effective, but the CFJ applied on the deflected flap is much more effective with flow attached up to the flap deflection angle of 60◦ . It has substantially higher lift coefficient enhancement and lower CFJ power consumption for the same Cµ . With Cµ = 0.08 and CFJ applied on the flap, the delta wing with AR of 2 improves CL by 113.1% at a flap deflection angle of 60◦, whereas (CL /CD )c is about the same as that of the baseline delta wing with no flow control at the same flap deflection angle. Trade studies are conducted to investigate the effect of delta wing incidence angle (β), flap deflection angle (δ), CFJ injection slot location, CFJ momentum coefficient Cµ . The trade study of the incidence angle shows that the CFJ used on the flap is effective at least up to β of 20◦ with the appearance of the delta wing leading edge vortex. The flap deflection angle study indicates that the baseline delta wing’s lift coefficient becomes flat when the flap deflection angle is greater than 30◦, whereas the delta wing with CFJ flap has the lift coefficient increased linearly to the deflection angle of 60◦ studied. The trade study of the injection location shows that the lift and drag coefficient are decreased about 5% when the injection is moved from upstream of the flap deflection shoulder to downstream of the shoulder, but the CFJ power coefficient is reduced by 50%. The injection momentum coefficient trade study indicates that the lift coefficient is enhanced most rapidly at low Cµ value range from 0.01 to 0.04 with a steep slope, whereas the CFJ power coefficient Pc increases at a slower pace. At Cµ of 0.03, the CFJ flapped delta wing achieves CL of 1.23, CL /CD of 4.21, and (CL /CD )c of 4.034. Compared with the baseline flapped delta wing with CL of 0.856 and CL /CD of 3.64, the CFJ delta wing achieves an increase of lift coefficient by 44% and CL /CD by 15.6% respectively with the CFJ power coefficient of 0.013. This study is only an initial effort to apply CFJ flow control to thin supersonic delta wing with a flap. It shows that CFJ is very effective to substantially increase lift coefficient at very low energy expenditure, which has great potential to enhance the supersonic aircraft’s low-speed performance.