Abstract: Binary asteroid explorations are of great scientific significance. It is extremely challenging for exploring binary asteroids because of the complex dynamical environments. Spherical harmonics method is adopted to represent the gravitational field of the binary asteroid. Five equilibrium points of binary asteroid system are obtained. The inner collinear equilibrium point L₁ is selected as the target point of the hovering flight. By considering the characteristic of impulsive thrusters, a kind of bang-bang controller which is simple and easily implemented for engineering operation is designed. This paper takes 69230 Hermes as an example, models it with two ellipsoids. Hovering flight over the point L₁ of the binary asteroid Hermes is numerically simulated to verify the effectiveness of the proposed method.