Focusing on the high-performance speed sensorless drive control of six-phase induction motor (IM), a second-order sliding mode (SOSM) model reference adaptive system (MRAS) estimator is designed to realize the optimized speed sensorless direct torque control (DTC) for six-phase IM. The super twisting algorithm is used in the new control scheme to propose a compensated flux observer, which is inherently an SOSM strategy. This observer is adopted as the reference model for MRAS speed estimation. In addition, a SOSM controller based on the upper twisting algorithm is designed for the speed outer loop in the DTC to improve the robustness to external load disturbances. Finally, the test results verified the SOMO MRAS speed sensorless DTC strategy can overcome the inherent chattering problem of classical sliding mode control, and has strong robustness to parameter uncertainties and dc bias.