Objective To investigate the incidence and clinical characteristics of immune-related adverse events (irAE) in the clinical application of immune checkpoint inhibitors (ICIs).Methods 646 patients with advanced malignant tumors who were treated by PD-1 and PD-L1 inhibitors between May 2020 and June 2022 were retrospectively analyzed in this study. The occurrence of their irAEs during treatment was observed and recorded, including the incidence rate, occurrence time, grade, etc.Results A total of 370 irAEs occurred in 259 of 646 patients, with an incidence rate of 40.1%. There were 266 (71.9%) irAEs of grade 1 and 2, and 104 (28.1%) irAEs of grade 3 or higher grade. The irAEs could involve all organs and systems, among which skin toxicities (15.6%) were the most common. 61 (23.6%) patients experienced multisystem irAEs. Patients with ≤65 years of age, drug combination, camrelizumab, sintilimab, or pembrolizumab were more likely to have multisystem irAEs. Hematological toxicities, hepatic toxicities, and cardiotoxicity occurred in the early time, averagely within 3 courses of treatment. Patients >65 years old and complicated with autoimmune diseases could also achieve clinical benefits with a good safety. Though incidence of irAEs was not associated with gender, age, complications, therapeutic regimens, tumor types, types of ICIs, and types of immune drugs (P>0.05), it was associated with the course of treatment (P<0.05).Conclusion ICIs are widely used in clinical practice, with a low incidence rate of serious adverse events and a relative safety. However, their adverse reactions can involve various organs and systems throughout the body, so it is important to get early identification, diagnosis and treatment of irAEs for these patients.