We have analyzed the asymmetric separation flow over a slender body at high angle of attack by numerical simulations aiming a control of the asymmetric vortices using a dielectric barrier discharge (DBD) plasma actuator. The Reynolds Averaged Navier Stokes/Large-Eddy Simulation hybrid method (RANS/LES) was adopted with the high-order compact spatial difference scheme. First, for investigating the characteristics of the asymmetric separation flow, the simulation of the flow field over the slender body was conducted for various angle of attack and bump height. Note that the bump is added near the body apex to simulate the symmetry-breaking imperfection. When the angle of attack or the bump becomes higher, the asymmetricity of vorticities becomes stronger. The side force has nonlinearity with the angle of attack or the bump height. Next, numerical simulations of the flow control using a plasma actuator were conducted. The side force coefficient can be continuously controlled in response to output power of the actuator within about ±1.0 on an average by the actuator's actuation at the aft body. However, the flow control effect is totally difference between starboard-side actuator's actuation and port-side actuator actuation. In addition, it is strongly influenced by the angle of attack.