Objective: To explore the influencing factors of happiness of nurses in Beijing Emergency Department and analyze their correlation with job burnout and mindfulness. Methods: From February 2018 to February 2019, 184 nurses in Emergency Departments of five 3A hospitals in Beijing were investigated by convenient sampling method. General data of nurses were collected by using self-made sociodemographic characteristics data. Mindfulness awareness questionnaire was used to evaluate nurses′ mindfulness thoughts. Nurses′ job burnout was evaluated by nurses′ job burnout questionnaire. The occupational well-being scale was used to evaluate nurses′ well-being, and then single-factor and multi-factor Logistic regression was used to analyze the influencing factors of nurses′ well-being in Beijing Emergency Department, and the mediating effect of mindfulness on job burnout and well-being. Results: The mindfulness scores of 184 nurses were (65.23±5.48), of which 54 (29.35%) had low mindfulness level, 80 (43.48%) had medium mindfulness level, and 50 (27.17%) had high mindfulness level. The emotional exhaustion (EE) score of job burnout was (29.76±4.32), depersonalization (DP) score was (9.66±1.30) and dimindished personal accomplishmen (tPA) score was (30.15±3.28), of which 63 (33.70%) were mild burnout, 70 (38.04%) were moderate burnout and 52 (28.26%) were severe burnout. The score of occupational well-being was (64.68±7.38). Univariate results showed that the factors affecting the happiness of nurses in Emergency Department included age, education level, professional title, working years, overtime work, monthly income and nature of employment. The scores of occupational well-being of Emergency Department nurses with mild, moderate and severe job burnout were (69.97±8.21), (61.72±9.21) and (56.41±7.02) respectively, with statistically significant difference (F=32.176, P<0.01). The occupational well-being scores of Emergency Department nurses with low mindfulness level, medium mindfulness level and high mindfulness level were (59.43±8.11), (63.72±9.51) and (76.41±6.98) respectively, the difference was statistically significant (F=40.291, P<0.01). Logistic regression analysis showed that working years, overtime work and job burnout were independent risk factors affecting the happiness of nurses in Emergency Department, while mindfulness was the protective factor. Occupational well-being of nurses in Emergency Department was proportional to mindfulness (r=0.812, P< 0.01), proportional to dimindished personal accomplishmen score in job burnout (r=0.713, P=0.008), and inversely proportional to EE score (r=-0503, P<0.01) and DP score (r=-0.614, P=0.012) in job burnout. The mediating effect of mindfulness was -0.179 4, accounting for 27.63% of the total effect. Conclusions Job burnout affects job burnout and well-being of nurses in emergency department, and mindfulness was the protective factor of well-being of nurses in emergency department.