Abstract: In this paper the approach of variable structure control strategy （VSCS） is applied to the control problems of large flexible spacecrafts taking the nonlinear forces into consideration. As the "assumed modes method" is employed, the measurement technique for obtaining the mode coordinates is studied. After the analysis of a suggested reaching law, the overall nonlinear feedback control law is established. This reaching law guarantees on one hand an exponential reaching velocity and a finite reaching time by diminishing the chattering phenomenon on the other hand. It is assumed that the torque may be more adequate than the force used as control actions. Some further efforts are needed as indicated in the conclusion.