This paper proposes a cascade proportional-integral continuous second-order sliding mode control method for brushless doubly-fed induction machine. This method consists of the speed out-loop proportional-integral controller and the current inner-loop sliding mode control. Proportional-integral controller provides references to the inner-loop sliding mode control with constraints according to the system requirements in terms of maximum current and speed limits. Sliding mode control method is designed to achieve excellent robustness and anti-interference ability, which is suitable for machines with nonlinear structures. Experimental results demonstrate the fast dynamic performance and excellent robust tracking of the proposed method.