To investigate the correlation between cognitive function and sleep quality, serum total tau protein (t-Tau), and phosphorylated Tau protein (p-Tau) in patients with chronic insomnia. Methods: We selected 52 patients with chronic insomnia for the insomnia group and 20 healthy individuals for the control group. Polysomnography and the Pittsburgh sleep quality index (PSQI) were used to assess objective and subjective sleep quality, and the Montreal Cognitive Assessment Scale (MoCA) was used to evaluate overall cognitive function. Serum t-Tau and p-Tau levels were measured. Results: PSQI score, sleep latency, and N1% of chronic insomnia patients were higher and sleep efficiency, N3%, and REM% were lower than those of the control group, and the difference was statistically significant (all P<0.05). MoCA total score, visual space and executive function, attention, and memory score of the insomnia group were lower than those of the control group (all P<0.05). Serum t-Tau and p-Tau of chronic insomnia patients were higher than those of control patients (both P<0.05). Correlation analysis showed that MoCA score was positively correlated with N3% and REM% and negatively correlated with PSQI score, N1%, and p-Tau level (P<0.05). Conclusion: Cognitive function of patients with chronic insomnia is impaired, and this is probably related to the reduced sleep quality, disordered sleep structure, and increased serum p-Tau protein level.