Aim: To investigate the prevalence of insomnia among front-line nurses fighting against COVID-19 in Wuhan, China, and analyse its influencing factors. Background: Insomnia is an important factor that can affect the health and work quality of nurses. However, there is a lack of big-sample studies exploring factors that affect the insomnia of nurses fighting against COVID-19. Method: This cross-sectional study using the Ascension Insomnia Scale, Fatigue Scale-14 and Perceived Stress Scale took place in March 2020. Participants were 1,794 front-line nurses from four tertiary-level general hospitals. Results: The prevalence of insomnia among participants was 52.8%. Insomnia was predicted by gender, working experience, chronic diseases, midday nap duration, direct participation in the rescue of patients with COVID-19, frequency of night shifts, professional psychological assistance during the pandemic, negative experiences (such as family, friends or colleagues being seriously ill or dying due to COVID-19), the degree of fear of COVID-19, fatigue and perceived stress. Conclusion: The level of insomnia among participants was higher than the normal level. Interventions based on influencing factors should be implemented to ensure nurses' sleep quality. Implications for Nursing Management: An in-depth understanding of the influencing factors of insomnia among front-line nurses can help nurse managers develop solutions to improve front-line nurses' sleep quality, which will enhance the physical and mental conditions of nurses and promote the quality of care.