Objective To investigate the present situation and reasons of emergency department overcrowding, and put forward effective mitigation strategy. Methods By using input-throughput-outputmodel and choosing the method of fishbone diagram analysis, detaily analysis factors of emergency department overcrowding, then implement three- dimensional intervention in hospital, department, personal. Results Patients who stay>48 h in the emergency department(ED) decreased from 11.9％(15225/127941) to 5.3％(7245/136698); patients who stay > 6 h in the Frist Aid Room of ED decreased from 54.6％(3016/5526)to 17.8％(987/5526), both have statistically significant (χ2=3705.04, χ2=1186.32, P<0.01);before the intervention the National ED Overcrowding Study (NEDOCS) index at 0900, 1300, 2100, 0100 was 234.22 ± 62.31, 253.55 ± 59.26, 303.73 ± 160.24, 187.36 ± 25.73; after the intervention the degree of crowdedness of ED at this four points of time was significantly alleviated, NEDOCS index was 193.09 ± 31.87, 187.09 ± 22.65, 187.36 ± 25.73, 154.03 ± 21.56;there were significant differences between the two groups before and after the intervention (t=2.35-4.32, P<0.05). Conclusions To study and discuss the reasons of emergency department overcrowding, it can effectively relieve the happening of emergency department overcrowding through comprehensive intervention measures such as improve the environment, optimize the process, strengthen emergency medical personnel training and management, improve the service level hospital auxiliary support system.