In this paper, optimal control of vehicle motion in obstacle avoidance with both steering and braking is researched. Previous researches have focused on the optimal motion states physically in emergency vehicle control. This research investigates the obstacle avoidance problem in the framework of an optimal control problem, that is, the vehicle is optimally moving at a target point under the minimization of an evaluation function. At first, the maximization problem of the lateral avoidance width is considered, and the area is derived where the vehicle can reach the target point stably. In the following, the minimization problem of the tire workload in the area is resolved. And the minimization problem of the velocity at the side of the obstacle is proposed. The problem is effective for reducing the damage in a collision, if the vehicle cannot avoid the obstacle. Some simulations are performed and the vehicle motion is analyzed in each problem.