Objective To analyze the causes for day surgery cancellations before admission or on the same day of operation, and put forward targeted measures to improve the medical resource utilization and patient satisfaction. Methods The basic information and clinical data of patients who had been scheduled for surgery in the Day Surgery Center of West China Hospital, Sichuan University between January 2018 and September 2021 were collected. The reasons for the surgery cancellations before admission or on the same day of operation were analyzed. Results From January 2018 to September 2021, a total of 45176 patients were successfully scheduled for day surgery, and 44300 patients completed surgery as planned. A total of 876 operations (1.94%) were cancelled after being scheduled, including 546 (1.21%) before admission and 330 (0.73%) on the surgery day. Ranked from high to low according to the cancellation rates, the top five departments were Department of Dermatology, Department of Vascular Surgery, Department of Hepatobiliary Surgery, Department of Otorhinolaryngology, Head and Neck Surgery, and Department of Gastroenterology, with a cancellation rate of 3.38% (8/237), 2.90% (25/863), 2.85% (101/3548), 2.48% (171/6893), and 1.91% (260/13578), respectively. In the reasons for cancellations, patient factors accounted for 57.31% (502/876) and medical management factors accounted for 42.69% (374/876). Conclusions The cancellations of day surgery mainly occur before admission, and are mainly caused by patient factors. It is necessary to strengthen the preoperative education for day surgery patients, and enhance the communication and cooperation between surgery physicians, nurses and technicians, in order to reduce the operation cancellation rate and make reasonable and efficient use of medical resources.