ObjectiveTo study the application and effectiveness of large class problembased learning (PBL) in the prejob training on healthcareassociated infection knowledge for medical students.MethodsMedical students of  2010 session were as the subjects of study, and were randomly divided into control group (n=163) and trial group(n=163). Control group adopted conventional lecturebased learning (LBL),  trial group adopted PBL. After finishing the course, two groups of students conducted closedbook exam,  and a questionnaire survey was also conducted among students in trial group.ResultsThe score of theoretical exam of trial group was higher than that of  control group (［87.99±4.49］ vs ［81.98±5.73］，P=0.001). Large class PBL  method can improve students’ active learning enthusiasm, promote initiative research and solving problems, promote communication and cooperation among students, as well as connection between learning and practice.ConclusionLarge class PBL is much better than LBC, but exam system of students’ participation before class needs to be explored constantly during the implementation process.