In order to improve the disturbance immunity and speed tracking performance of modular multilevel inverters in the face of external disturbances, an MMC control strategy based on improved terminal sliding mode auto disturbance rejection control is proposed. Firstly, the mathematical model of MMC is established, and then the Cascaded nonlinear Extended state observer are designed to estimate the perturbations in real time and add them into the system model. And the linear error state feedback controller adopts terminal sliding mode control to provide feedback based on the observed perturbations and state errors, which compensates the impact of perturbations on the system performance and improves the closed-loop stability and robustness of the system. Meanwhile, in order to avoid the singularity problem, the sliding film surface adopts the integral terminal sliding mode form, and in order to reduce the chattering problem of the traditional sliding mode control, the convergence law adopts a new type of variable gain exponential convergence law, which can weaken the phenomenon of the chattering caused by the high gain of the discontinuous term. Finally, Matlab is used to conduct simulation experiments, and the grid-connected current of the proposed control strategy is stabilized at 0.015s, and the THD value is 1.85%, which meets the grid-connected conditions. The proposed control strategy is compared with the terminal sliding mode control, adaptive control and PI control through the power mutation and grid voltage dips. The experimental results show that the proposed control strategy has good anti-interference performance and speed tracking performance.