Along with the increasing of infections of COVID-19, nurses are needed more in caring patients with COVID-19. The aim of this study is to explore the real intention and influencing factors of the nurses' willingness to participate in public health emergency in facing the COVID-19. A total of 10 nurses who volunteered to care patients with COVID-19 were selected. Data were collected by semi-structured interviews and analyzed by content analysis method based on the theory of planned behavior. Three main categories were attitude, subjective norms and perceived behavior control. Under the first category, two subcategories were included: nurses' personal and professional value expectation, patriotism. Two subcategories were yielded for the second category: support from family and friends, role model impact of important people. In addition, three subcategories were identified for the third category: physical condition, professional knowledge and skills, national measures and incentive policies. Nurses with high willingness have seven features: high value expectation, patriotism, generous family support, good physical condition, experienced professional knowledge and skills, awareness of national measures and incentive policies. Combined with our previous quantitative study, developing tailored training programs to improve nurses’ professional value expectation, knowledge and skills in coping with unwilling attitude and weak perceived behavior control are effective ways.