Inclusion Criteria:  Age ≥ 65 years old and ≤ 85 years old; Selective non-cardiac major surgery; Informed consent and voluntary participation in the trial; ASA class I-II; Anticipated operation duration ≥ 2 hours; No plan to ICU after operation.  Exclusion Criteria:  Neurosurgery; Patients with neurological and mental diseases: such as basal ganglia disease, Parkinson's syndrome, severe central nervous depression, Alzheimer's disease , etc; Patients with prolonged Q-T interval, cardiac repolarization disorder and other severe arrhythmia; Patients with severe cardiopulmonary disease, liver and kidney dysfunction; Allergic or contraindications to droperidol or fentanyl citrate; Admitted to ICU after operation. Operation duration < 2 hours;