OBJECTIVE To learn the common proto col deviation （PD）in the process of drug clinical trials and discuss the methods and precautions for preventing and reducing PD so as to provide reference for the standardization of drug clinical trials. METHODS According to Good Clinical Practice ，Notice on Issuing Guidelines for Planning and Reporting of Data Management and Statistical Analysis of Drug Clinical Trials ，Guidelines for Ethical Review of Drug Clinical Trials ，ICH E 3，ICH E 6（R2）and other regulations ，the PD reported in the relevant projects managed by the author from March 2017 to February 2022，as well as the PD found in the submission materials and project quality control ，were sorted out and statistically analyzed. RESULTS & CONCLUSIONS A total of 39 drug clinical trials were included ，and 212 subjects were selected. In all projects ，258 PDs were reported，including 28 major PD （accounting for 10.85％）and 230 ordinary PD （accounting for 89.15％）. The report of PD mainly included missed inspections/tests （93 reports，accounting for 36.05％），lack of visits （36 reports，accounting for 13.95％）， inspection/testing out-of-window （29 reports，accounting for 11.24％），dosage and usage of test drugs （28 reports，accounting for 10.85％），drug over-temperature/missing temperature （21 reports，accounting for 8.14％），etc. Avoiding and reducing the occurrence of PD requires the efforts of multiple parties ：the sponsor designs a reasonable protocol with appropriate interview rate and window period after listening to the opinions of multiple parties ；the investigators and clinical research coordinator should strengthen their own learning and training ，and be familiar with the protocol ，Good Clinical Practice and corresponding regulations；the compliance education of the subjects should be strengthened ；the institutional offices and ethics committees should conduct multi-angle and whole-process supervision and management when a drug clinical trial is approved ，in progress ，and jsyj- concluded，to ensure the safety rights and interests of the zdcxX0079） subjects and the quality of clinical trials. On this basis ，all parties should communicate effectively and timely ，report PD in time ，and conduct special studies on major PD that have com occurred and key links that are prone to PD.