Objective To observe the effect of subanesthetic s‑ketamine on the electroencephalography (EEG) pattern of sevoflurane general anesthesia, and to find the proper indicator for evaluating the anesthetic depth of s‑ketamine‑combined anesthesia. Methods A total of 10 Han nationality patients who were scheduled for gynecological laparoscopy in the First Affiliated Hospital of the Air Force Medical University from November 2020 to December 2020 were enrolled. According to the random number table method, they were randomly divided into two groups (n=5): the s‑ketamine group (group K) and the control group (group S). The patients were administered with s‑ketamine (0.15 mg/kg) or normal saline with the same volume 30 min after operation, respectively. Sevoflurane inhalation and remifentanil intravenous pump were used for anesthesia maintenance. Their general information were observed, and EEG data were collected during the whole process of anesthesia. The changes of edge frequency, anesthesia index (Ai) and phase amplitude coupling were analyzed. Results There were no statistical differences in age, body mass index (BMI), mean arterial pressure (MAP) and heart rate between two groups before and after treatment (P>0.05). The mean power spectrum of group K decreased in the low frequency wave and increased in the high frequency wave after administration. Particularly, the edge frequency and Ai value of EEG significantly increased after administration (P<0.05). There was no statistical difference in EEG power spectrum of group S before and after administration (P>0.05). The changes of edge frequency and Ai in group K were significantly higher than that in group S (P<0.05). There was no statistical difference in the coupling strength of δ wave phase and α wave amplitude between group K group and group S (P>0.05). Conclusions The subanesthetic s‑ketamine can change the EEG pattern of sevoflurane general anesthesia, without effects on the depth of clinical anesthesia. δ‑α phase amplitude coupling index may rationally reflect the actual depth of subanesthetic s‑ketamine‑combined anesthesia.