BackgroundWith frequent conflicts, natural disasters, and public health emergencies globally, mobile medical teams (MMTs) are becoming increasingly critical. Importantly, the competency of critical care nurses in MMTs can substantially affect the effectiveness and quality of its rescue efforts. Yet, these nurses' competencies are not well understood.AimThis study examined the competencies of critical care nurses in MMTs using the Onion Model.DesignA qualitative descriptive method was used to describe the competencies of Chinese MMT critical care nurses.MethodsFrom April to May 2022, a convenience sample of 18 participants (14 critical care nurses and 4 surgeons) from 10 MMTs was recruited for semi‐structured interviews. Deductive and inductive coding methods were combined for content analysis.ResultsIn total, 29 competencies were identified, which were grouped into four major domains using the Onion Model. From the outer to inner layers, these domains were knowledge and skills, professional abilities, professional quality, and personal traits. Several novel competencies emerged, including field medical equipment operation skills, on‐site hazard identification and safety prevention skills, triage knowledge, and field survival skills.ConclusionsUsing the Onion Model, this study furthers the understanding of the competency of critical care nurses in MMTs, especially by revealing the novel competencies. Further, the results can be used to recruit, evaluate, and train critical care nurses for MMTs.Relevance to Clinical PracticeUnderstanding MMT critical care nurses' competencies can help managers plan and provide relevant training and education before deployment, which can improve nurses' performance, and especially reduce the mortalities and disabilities from trauma.