Objective To analyze the distribution characteristics and risk factors of extended stay over 30 days at tertiary comprehensive hospitals, and explore methods of shortening average length of stay(LOS).Methods Homepage of all inpatients discharged from October 2014 to October 2015 of 31 tertiary comprehensive hospitals in Shanxi province were collected.39 234 cases of these inpatients stayed over 30 days and their case information was complete.A generalized linear model was used for risk factors analysis.Results With the extension of LOS, most of the inpatients with extended stay were found during their 30th-40th days, accounting for 50.21% of all and constituting the highest daily costs as well.The ratio of inpatients decreases with their LOS, and its distribution presents a positive skew in entirety.Distribution of inpatients over 30 days identified urban employees under medical insurance accounting for the highest ratio among all payment categories,and those from the department of orthopedics for the highest ratio among all departments, while those of diseases from injury and poisoning accounting for the highest ratio among all disease categories.The findings indicated ten important factors for extended stay, namely gender, medical payment category, ICD, inter-department transfer, nosocomial infection, and clinical pathway.Conclusions To strengthen management of specific departments and inpatients, focus on key process of medical quality, and accelerate medical insurance payment reform can effectively control extended stay.