Two-wheel mobile robot (2WMR) has been widely investigated for its variety of different applications. This paper focuses on a two-wheel robot with a pair of auxiliary arms, aiming at keeping the body of robot upright during acceleration and deceleration. The model dynamic of 2WMR with auxiliary arms has been derived and the relationship between acceleration and center of gravity(COG) is investigated. A controller based on adjusting COG and linear quadratic regulation(LQR) is proposed in this paper. The effectiveness of auxiliary arms and the corresponding controller is confirmed by numerical simulations. By actively rotating the auxiliary arms to adjust the position of COG, the 2WMR accelerates and decelerates rapidly with the body almost upright all the time in simulation.