In national and social crises, high-quality nursing education in the undergraduate program is essential to improve the clinical nursing competency and problem-solving ability of nurses who are nursing mediators. The purpose of this study is to develop and apply an online nursing training simulation program for nursing students and test its effectiveness. The study used a quasi-experimental, single group and a pre and posttest design. The program improved the participants' clinical competency and problem-solving ability scores, and it was found that the online nursing training simulation program was an effective intervention for the clinical performance and problem-solving ability of nursing students. The online nursing training simulation program developed in this study enables repeated training while minimizing the burden on learners. In addition, it can be applied without time and space restrictions in a continuous infection situation such as COVID 19. In the future, based on the results of this study, it is necessary to develop various online nursing practice contents. In addition it is suggested that long-term follow-up studies will be conducted to verify the persistence of effects through repeated measurements.