In this paper, sliding mode control based on power reaching law for an n-order disturbance system under denial-of-service(DoS) attacks is studied. First, the states predictor is constructed to reconstruct the system states lost during the active periods of attacks. Based on the predictor states and non-smooth function, a power reaching law sliding mode controller under energy constrained DoS attacks is designed, and the sufficient conditions for the stability of the system are further analyzed. Then, it is proved that the power reaching law sliding mode control method still maintains the strong anti-interference ability of the non-smooth controller when the system has external disturbance. Finally, the results of the theoretical proof are verified by numerical simulation.