The arc discharge plasma actuator (ADPA) has wide application prospects in high-speed flow control because of its local heating effect and strong disturbance. In this paper, the influence of ambient pressure, which ranges from 3 to 20 kPa, on the performance of a two-electrode ADPA is investigated by a schlieren system. The duration of the arc heated region, as well as its area, is extracted by image processing. As the ambient pressure increases, different flow field evolutions occur. The duration of the ADPA heated region increases with the ambient pressure. The maximum duration reaches 1185.3 μs at 20 kPa. The velocity of the discharge-induced blast shock wave first decreases gradually and then remains at 345 m/s for all air pressures. The blast shock wave has a higher velocity at lower pressures when it is freshly produced. A maximum blast shock wave velocity of 582 m/s is observed at the pressure of 7 kPa. The arc heated region is not sensitive to ambient pressure, but the deposited energy from the arc increases when the pressure increases. KEYWORDS ambient pressure, arc discharge plasma actuator, performance, schlieren method 1