A control system and ground pilots who operate the system are necessary to control an unmanned vehicle. This paper describes a Ground Control System(GCS) of the unmanned airship developed at KARI. The system is capable of mission planning, real-time data processing, remote real-time data analysis, and data storage and extraction. We estimate the performance of the system and verify its reliability using real-time simulation software. The software relies on a priority-based multitasking algorithm. No task has delay time and deadlock with semaphore, all of the ground system works in stable during the test flight.