Online and offline mixed teaching is increasingly becoming the main trend of teaching reform and development in colleges and universities. This paper focuses on the offline teaching and online synchronous discussion and assessment for the course of “Radiation Measurement and Protection” . Through pre-class preparation, in-class teaching and after-class review, this paper explains the process of mutual dependence and complementarity of mixed teaching. In the online course, students’ pre-class preview task, in-class knowledge point discussion task, after-school homework, online guidance and attendance statistics are added, and the learning analysis table of each student is generated in realtime, so that teachers can understand students’ learning situation in time. Through the three criteria of online evaluation, offline evaluation and the final-examination, teachers can focus on evaluating students’ learning processes, thus effectively mobilizing students’ enthusiasm and initiative in learning. Through the practice of blended online and offline teaching in recent years, the teaching effectiveness has been significantly improved.