In order to overcome the disadvantages of large torque and current ripple in direct torque control of induction motor, an improved active disturbance rejection control (ADRC) speed controller was designed to replace the traditional PI controller. According to the mathematical model of induction motor and sliding mode variable structure control theory, a new sliding mode controller based on torque error and stator flux squared error was designed. In order to estimate the applied load torque and reduce the system uncertainties, a load torque observer based on supertwisting algorithm was designed. Supertwisting stator flux observer was designed to improve the observation accuracy. The steadystate optimal stator flux was obtained through optimization calculation and introduced into the speed regulation system. Simulation results showed that this control strategy could effectively reduce torque and current ripple, and had inhibitory effect on external disturbance. At the same time, it could reduce the motor running loss, and had good dynamic and steadystate performances.