Considering the difficulties，which the design of fuel control system of aero engine may meet in face of a second-order unsteady actuator，the variable-structure control method，which makes the second-order unsteady actuator into an assured first-order inertial element, is introduced. This method is especially suitable to drive a pulse proportional valve, for it makes full use of its advantage, invariance, while having dodged its inherent disadvantage, chattering. Some key technologies to solve specific problems to implemente variable structure control on pulse proportional valve，such as precision problem of differential, and some necessary conditions in relation to the feasibility of this method are also specified. The patent number of this method : 201010610220.8。