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With the growing prominence of peripheral nerve stimulation technology, the clinical applications and potential neurophysiological mechanisms of external trigeminal nerve stimulation (eTNS) have garnered increasing attention. Despite its status as the sole neuromodulation method commonly employed in sleep, no studies have explored the effects of eTNS at varying frequencies on sleep activities. This study aims to investigate the regulatory effects of high-frequency and low-frequency eTNS on sleep activities using polysomnography. In this within-subjects experiment, 20 participants underwent a night of adaptation sleep, followed by 8-h sessions of sham, 120Hz-, and 2Hz-eTNS interventions in a randomized order in the sleep laboratory, with polysomnographic signals collected throughout. The results indicated that 120Hz-eTNS significantly improved sleep efficiency, increased N2 sleep proportion, and reduced sleep latency, without significantly affecting sleep stage transition probabilities, sleep duration, or sleep-specific wave activities. Conversely, while 2Hz-eTNS did not impact sleep efficiency or latency, it increased the proportion of N3 sleep, stabilizes N3 sleep, and enhanced the survival probability of N3 and REM sleep duration. Additionally, it increases the density of slow oscillations (SOs), improved the coupling ratio of SO-spindles, and enhanced coupling timing accuracy. These findings suggest that eTNS during sleep can indeed modulate sleep activities, with different frequencies exerting distinct regulatory effects. This may hold significant value for advancing the clinical application and efficacy of eTNS. • This study used overnight polysomnography to explore eTNS effects on sleep, revealing significant frequency-dependent modulations. • Findings demonstrated that 120Hz-eTNS improved sleep efficiency and latency while 2Hz-eTNS mainly influenced N3 stage sleep. • Additionally, 2Hz-eTNS enhanced slow oscillations' (SOs) density, improved SO-spindle coupling ratio and timing, effects not seen with 120Hz-eTNS. • This study highlights eTNS parameter effects, underscoring its potential for personalized modulation and clinical applications. [ABSTRACT FROM AUTHOR]