In the context of COVID-19, a mixed-mode teaching was explored. The reforms for teaching content and mode were introduced through a case of Indoor Air Environment, which is a core curriculum for postgraduate students of HVAC program. The innovations included teaching content restruction based on online teaching mode, interaction design based on an intelligent teaching platform, and mixed-mode teaching design based on Flipped Classrooms. The ideological and political elements were deeply researched based on network resources for COVID-19, and were integrated into in a CFD simulation teaching case to reshape the teaching contents. Flipped Classrooms were adopted in the process management for curriculum paper to realize mixed-mode teaching and improve students" learning achievement. Finally, a good teaching effect has been achieved after a semester of teaching practice.