Abstract: Aiming at the problems of vulnerable high-speed shaft/output mechanism, oil leakage of floating seals and excessive box temperature existing in the cutting reducer of high-power horizontal axis roadway driving machine, this paper designs a new-type high-reliability structure, and proposes a four-stage transmission scheme consisting of helical gear-bevel gear-NGW planetary-fixed-axis gear train. A composite sealing structure combining metal sealing rings and dust-proof rings is adopted, and an independent forced lubrication-cooling system with multi-chamber partition is developed. This structure can realize highly reliable connection with the cutting drum, and effectively restrain dust intrusion and medium leakage. Under the combined effect of multi-chamber isolation and forced cooling, the box temperature drops from 85 ℃ to below 65 ℃ under typical working conditions, and the expected service life of sealing components is increased by more than 30%. The results show that the proposed structure can effectively solve the engineering problems such as oil leakage and excessive operating temperature, and is suitable for high-power hard-rock tunneling conditions.