The COVID-19 pandemic has brought disruptions and constraints to K-12 STEM education, such as the shortened classroom time and the restrictions on classroom interactions. More empirical evidence is needed to inform educators and practitioners which strategies work and which do not in the pandemic context. In response to the call for more empirical evidence and the need for cultivating responsible and competent 21st century citizens, we designed and implemented a transdisciplinary STEM curriculum during the COVID-19 outbreak. In order to facilitate the smooth delivery of the learning contents and authentically engage learners in the learning process, multi-model video approaches were employed considering the characteristics of three disciplines, STEM, social service, and writing, as well as learner diversity. Pre- and post-test results indicated that students' transdisciplinary STEM knowledge improved significantly after completing the curriculum. The integration of STEM, social service, and writing disciplines promoted the growth of students' empathy, interest, and self-efficacy. Consistent with the quantitative results, students responded in the interview that their STEM knowledge and empathy were both enhanced. Some implementation strategies introduced in the current study are also applicable when the standard teaching order is restored in the post-COVID-19 era.