Background: Medication errors are a common problem in Chinese hospital, with potentially harmful consequences for patients. The objective of this study was to analyze the cause of typical serious medication errors in some first-class provincial hospital to prevent medication error and improve rational use of drug and ensure patients administration security. Medication errors were collected between September 1, 2012 and August 31, 2013. 332 cases’ medication errors were categorized as harmful or not according to NCC MERP’s Index and other indexes such as type of error and causes of error. We focus on analyzing the 3 serious cases (0.9%, n = 3) among the all MEs that may have contributed to or resulted in temporary harm to the patient and required intervention, including the process and the cause and the background of the errors. The case analysis reminds us to pay more attention to prevent medication errors. The preventive medication error’s measures are explored through the analysis of the causes, such as forcing functions and constraints, automation and standardization, double-checking systems, rules and policies, information and more careful working. Conclusion: This analytical study demonstrates that medication error is an objective existent in hospital. It is especially important to ensure patient medication safety for reporting and analyzing medication error in order to explore measures preventing medication error.