Wide-area control is a promising technology in the next generation of bulk power system. A wide-area damping control（WADC） system has recently been developed by China Southern Power Grid Ltd. Co.， to enhance the damping performance of inter-area oscillations in China Southern Power Grid. The WADC system uses modulation of two HVDC systems for improving power system dynamic stability. The control system comprises phasor measurement units（PMUs） at six 500 kV substations， fiber-optic communications， real-time control computers， control units at rectifier station and interface between HVDC and WADC. This paper introduces the design aspects of the WADC system and the subsequent implementation issues. Results of open-loop trial operation and closed-loop testing in the field are analyzed and used to show the effectiveness of the system.