Objective To explore the occupational fatigue of nurses in emergency departments based on the effort-reward imbalance system，analyze its risk factors，and provide reference for exploring effective risk management strategies for fatigue in emergency department. Methods The interview outline was constructed under the guidance of the three factors of the effort-reward imbalance model，namely intrinsic drive，extrinsic effort and extrinsic reward. The semi-structured interview method was adopted to conduct in-depth interviews with 12 emergency department nurses from two tertiary class A hospitals in Kunming from August to October 2022，and the collected data were analyzed using Colaizzi’s 7-step analysis method for phenomenological data. Results The extracted topic included three dimensions and a total of 6 factors. There are two internal driving factors：efficient team cooperation and rapid improvement of personal ability. There are three external factors：intense work load，conflicting experience with patients，and excessive training input. And it has an extrinsic reward，meaningful recognition. Conclusion The study found that efficient teamwork，rapid improvement of personal ability and meaningful recognition can promote the continuous work of emergency department nurses，but high intensity of workload，conflict experience with patients， and excessive training investment will aggravate the occupational fatigue experience of emergency department nurses. It is necessary to identify the occupational fatigue of nurses in time and understand the influencing factors， so as to adopt targeted pre-control strategies to promote the physical and mental health of nurses，increase the empathy，and reduce the brain drain of emergency department.