Abstract: To investigate the cooling performance of thermosyphon-ventilated plate composite subgrade in permafrost regions， field experiments were conducted on a highway section between the 109 Junction at Erdaogou Military Station and Zhiduo along the S224 Line in Qinghai Province. The research reveals that the composite structure achieves three-dimensional optimization of the subgrade temperature field by establishing a tri-integrated regulation mode of "active cooling guidance - passive heat dissipation - cooling energy reserve". Based on the field-monitored temperature data and ground temperature measurements， this study analyzed the cooling performance of both the thermosyphon-ventilated plate composite subgrade and the ventilated plate subgrade. The research findings indicated that the composite subgrade， through a synergistic mechanism of "thermosyphon phase-change cooling + ventilated plate-enhanced heat dissipation"， extended the heat transfer influence depth to -6 m during the cold season， forming a core cooling reserve layer spanning 2 to 6 meters in depth with a cooling energy reserve of 5220 J/kg， representing a 35.5% increase compared to the ventilated plate subgrade alone. Moreover， monitoring data revealed that the composite subgrade stabilized the permafrost table at a distance of 2.0 to 2.5 meters from the road surface， representing a 0.5 m uplift compared to the ventilated plate subgrade alone. The thermosyphon system maintained continuous operation for 215 days during the cold season. This study proposes a novel technical solution utilizing the synergistic effect of "thermosyphon phase-change cooling + ventilated plate-enhanced heat dissipation" for highway construction in discontinuous and continuous permafrost regions （particularly ice-rich and ice-saturated frozen soil areas） where the annual average ground temperature on the Qinghai-Tibet Plateau is ≤ -1 ℃.