In order to deeply explore the factors that affect the occurrence of illegal events in drug clinical trials， this study used the grounded theory to sort out and analyze the illegal records of drug clinical trials during 2017—2019 in a large general hospital in Anhui Province and construct a model of influencing factors of illegal events in drug clinical trials. The results showed that “pre?control of drug clinical trial risks” and “prerequisite basis for drug clinical trials” had significant impact on the occurrence of plan violations. It is recommended to improve the research environment and resource conditions， strengthen the relevant training of researchers and research teams， and rationally design research plans. It is suggested to establish a safety monitoring system， improve the reporting and handling mechanism for adverse events， guide researchers to deepen the transformation of moral concepts， and provide some ideas and suggestions for reducing the occurrence of illegal events in clinical trials and controlling the quality of drug clinical trials.