Abstract: The controllability of large-scale nonlinear system is discussed by virtue of the weak controllability of common nonlinear system to define the weak controllability of large-scale nonlinear system, while the large-scale nonlinear system is weakly controllable since the nonlinear subsystems are the same. The necessary and sufficient condition of a weakly controllable large-scale nonlinear system is that every subsystem of the large-scale nonlinear system is weak controllable. It is proved that a large-scale nonlinear system is weak controllable if only every Lie Algebraic expression of controllability of subsystem can satisfy its controllability rank condition, regardless of the controllability of the large-scale nonlinear system, as well as a nonlinear system that is weak controllable if its Lie Algebraic expression of controllability can satisfy its controllability rank condition.