The emphasis of building thermal engineering on the passive construction of the built environment is in line with China’s “double carbon” policy. It also fits the background of constructing “emerging engineering” and “double first-class” colleges and universities. Consequently, building thermal engineering has been attracting an increasing number of interdisciplinary students for graduate education. Setting appropriate transitionary topics can help large-span interdisciplinary students to quickly enter the field of building thermal engineering and achieve interdisciplinary integration. This paper firstly analyses the necessity and significance of transitional topics, then discusses the key points of transitionary topics in the process of large-span interdisciplinary postgraduate training in terms of topic selection criteria, principles and methods, as well as evaluation and adjustment during the process. Finally it uses two typical cases to provide a detailed analysis of the idea of transition topics and their training effectiveness. Transition topics are not only a common challenge for supervisors and students, but also useful to promote cross-disciplinary integration, which should be customized according to the specific situation of students and the research direction of supervisors and groups. The results of this paper can effectively promote the cultivation of large-span interdisciplinary students in building thermal engineering, and at the same time provide reference for other disciplines.