This document is a master's thesis from February 14, 2007 on the development of an indoor balloon robot flight control system based on PID control. The system aims to allow balloon robots to freely move in 3D space. The control system consists of motion design to achieve flight units and a controller to reach target states based on calculating velocity deviations from target and actual states. Experiments on station-keeping, rotation, and straight-line motions demonstrated the system's effectiveness for potential indoor balloon robot applications.