Compared to a single flying robot, the swarm can significantly enhance robustness and capability in real-world missions. However, the overall flight duration of such system is still heavily constrained by the energy system, typically composed of lithium batteries. To cope with this issue, this paper develops an autonomous mobile charging station for the aerial swarm system to improve the endurance so that the system satisfies the need for the long-term mission such as surveillance and monitoring. The mobile charging station has the ability of environment perception and obstacle avoidance. On this basis, a charging module with multiple contact points is developed, and a motion tracking algorithm is proposed accordingly to support precise landing on the charging module. To further improve the flexibility in on-going real-world missions, a charging schedule and an area coverage policy are also proposed. A prototype system is built to verify the effectiveness of this system and experiments demonstrate the system could cover an area of interest completely and efficiently.