The concept of energy angle has been utilized for airspeed controlling of civil aircraft and trigging low energy warning signal when aircrafts approach the airports.The definition of energy angle is introduced,and the principle of airspeed control and the method utilizing energy angle to trig low energy warning signal are presented.The flight control system based on Total Energy Control System(TECS) is the evolution of concept of energy angle.Compared with traditional flight control system,TECS based flight control system has the advantages as follows: simpler configuration,convenient emigration,and less couple of speed control and altitude control.It is also possible to broaden the application of energy angle concept to more areas.