The CG envelope of civil aircraft is the security of safe use of aircraft. It is an insurmountable boundary of plane in flight. The design quality of CG envelope does not only affect the flight performance of aircraft, but also its economy and security. Its determination requires the multi-disciplinary trade-offs of General Configuration, aerodynamics, stability, maneuverability, performance, strength, weight and etc. This article, which gives brief analysis on the influence of CG on the performance, the constraints of CG boundary and how to design a good CG envelope, provides reference on the design of CG and CG envelope of civil aircraft.