Center of gravity (CG) design is a substantial part of aircraft design while fuel consumption is an important factor that changes the CG of an aircraft. Maintaining system CG within reasonable scope through systematic layout and fuel supply and transfer procedures is a key objective of fuel system design. As less artificial intervention is applicable to unmanned aerial vehicle (UAV), automatic matching and control of CG seem to be particularly important. Based on the design of a UAV fuel system, this thesis sets forth principles of CG control of the UAV and verifies the validity of such control. The study in this thesis may be used as reference in the design of UAV fuel system.