With the rapid penetration of electric vehicles (EVs), the security of EV charging systems is becoming an important issue. This paper addresses cyber-physical protection of EV charging systems from the perspective of control theory. By using a residual generation technique, an attack-resilient EV charging system is designed, which detects false data injection under the denial of service (DOS) attack. The effectiveness of the proposed attack-resilient EV charging system is verified experimentally by using a hardware-in-the-loop testbed, developed by the IEEE 802.15.4 wireless sensors.