During the pandemic of coronavirus disease 2019 (COVID-19), the Chinese Ministry of Education put forward the requirement of turning offline education into online teaching to universities. Our department positively responded and rapidly mobilized to establish an online teaching system of medical immunology based on the small private online course (SPOC) model, which has a main body of the SPOC model with "video course as the main part, supplemented by online Q&A". The system also has feedback improvement sections of online discussion and chapter tests and evaluates the quality and effect of teaching with students' group display, course examination, and questionnaires. At the same time, the COVID-19 hotspot is also organically combined with immunological knowledge throughout the online teaching. In this process, our department continuously summarizes experiences and discovers problems. Herein, we generalize and sort out the exploration and practice of constructing the online teaching system, to carry out offline teaching after the pandemic and to continue this teaching model in the future, for reference and guidance.