Background Effort-reward imbalance is an adverse psychological response to working conditions that has several negative effects on nurses. However, there is little research on effort-reward imbalance and its influencing factors among nurses in emergency departments. This study aimed to understand the current situation of effort-reward imbalance and explore its influencing factors among emergency department nurses in China. Methods From July to August 2018, a structured online questionnaire survey was conducted among emergency department nurses in China. Data were collected from emergency department nurses employed in hospitals providing pre-hospital care in China. The questionnaire consisted of sociodemographic characteristics, work-related factors and effort-reward imbalance. A descriptive analysis and a binary logistic regression were conducted to explore the effort-reward imbalance and its influencing factors among emergency department nurses. Results The study involved 17,582 emergency department nurses; notably, the prevalence of effort-reward imbalance was 59.66%. The participating nurses who were males, aged 25 to 34 years, whose educational level was a bachelor degree or above, who had a junior or above title, who had longer years of service, and who had suffered verbal or physical violence in the past year had a higher risk of effort-reward imbalance. Furthermore, the nurses with a high monthly income, who believed that the number of nurses met the department's demand had a lower risk of effort-reward imbalance. Conclusions Effort-reward imbalance was prevalent among emergency department nurses in China. Measures such as adjusting the night shift frequency, increasing the number of nurses, raising salaries and reducing workplace violence should be considered to reduce the level of effort-reward imbalance.