Due to the non-cytopathogenic replication of classical swine fever virus (CSFV) in cell culture, large-scale production of CSFV using bioreactor system remains the problem of monitoring the time of maximum virus production for optimal harvest. In this study, we proposed the application of real-time quantitative PCR assay to monitoring the progress of CSFV infection and yield determination in large scale. The region of NS5B of CSFV responsible for CSFV genome replication was used for the designation of primers and probe. Viral titers determined by the real-time quantitative PCR assay were compared with the conventional cell-culture based method of immunofluorescent staining. Results from large scale production show that a similar profile of CSFV production was successfully outlined by real-time quantitative PCR and virus yields were comparable to the results from immunofluorescent staining assay. By using this method, an optimal harvesting time of the production could be rapidly and precisely determined leading to an improvement in virus harvest.