Abstract： Objective： To observe the clinical effect of modified Suanzaoren tang on cognitive function in patients with chronic insomnia of yin deficiency with effulgent fire type and its possible mechanism. Methods： In accordance with the inclusion criteria，a total of 70 cases were included and divided into the western medicine group and the Chinese medicine group according to the random number table method. Finally， 67 cases were included， including 33 cases in the western medicine group and 34 cases in the Chinese medicine group. The western medicine group was treated with estazolam tablets， and the Chinese medicine group was treated with modified Suanzaoren tang. Both groups were treated for eight weeks. The objective indexes of sleep and the evaluation indexes of cognitive function in the two groups were observed. Results： ① According to the Pearson correlation， the scores of Montreal Cognitive Assessment(MoCA) were positively correlated with the total sleep time， the deep sleep time and rapid eye movement(REM) sleep time， and negatively correlated with the awakening time， the time of first falling asleep and the light sleep time. ② After treatment， in the western medicine group， the total sleep time and the light sleep time were prolonged， and the REM sleep time， the awakening time and the time of first falling asleep were shortened，the difference being significant(P＜0.05)；there was no significant difference being found in the comparison of the deep sleep time before and after treatment(P＞0.05). After treatment，in the Chinese medicine group，the total sleep time and the deep sleep time were prolonged，and the time of first falling asleep were shortened，the difference being significant(P＜0.05)；there was no significant difference being found in the comparison of the light sleep time，the REM sleep time and the awakening time before and after treatment(P＞0.05). After treatment，there was no significant difference being found in the comparison of each index between the two groups(P＞ 0.05).③After treatment，the MoCA score in the western medicine group was significantly decreased when compared with that before treatment， the difference being significant(P＜0.01)； the MoCA score in the Chinese medicine group was increased，the difference being significant(P＜0.05)；there was significant difference being found in the comparison of the MoCA scores between the two groups(P＜0.05). ④Before and after treatment， there was no significant difference being found in the comparison of Mini- mental State Examination(MMSE) scores between the two groups(P＞0.05). After treatment，there was no significant difference being found in the comparison of MMSE scores between the two groups(P＞ 0.05). Conclusion：Mild cognitive dysfunction is the main manifestation of chronic insomnia，and the cognitive impairment is related to sleep time reduction，sleep structure damage，and sleep fragmentation. Modified Suanzaoren tang can improve mild cognitive function of patients with chronic insomnia，and may reverse the plight of deterioration of cognitive function of the patients after receiving benzodiazepines treatment. The mechanism may be related to the increase of the deep sleep time and the improvement of the sleep structure.