Half-wavelength AC transmission (HWACT) provides an alternative for remote transmission scenario due to its characteristics. However, the problem of secondary arc current limits the development and application of HWACT. The existing techniques have drawbacks when applied in HWACT system. In order to solve the problem, the distribution characteristics of secondary arc current in HWACT are analyzed, based on it the suppression technique using modular multi-level converter (MMC) is proposed. The control strategy and parameters of MMC are designed to compensate secondary arc current in HWACT system. Furthermore, a compensation scheme is proposed to reduce the capacity of MMC by switching passive components independently. Finally, simulations are carried out in PSCAD/EMTDC to verify the proposed method. The results show that the proposed technique can limit secondary arc current in HWACT system, and speed up the arc extinction and improve the fault recovery efficiency of the system.