Abstract: Trichogramma ostriniae is an important parasitic natural enemy. Age and refrigerating time are important factors affecting its viability. In order to figure out the impacts of age and refrigerating time on viability in T. ostriniae at low temperature, orthogonal test and variance analysis were carried out to analyze the differences of parasite number, emergence number and emergence rate in different age or at different refrigerating time. The results showed that the maximums of parasite number, emergence number and emergence rate were separately in 4 days, 2-3 days, 1-2 days of age when refrigerated at different stages. The maximums of parasite number and emergence rate were on 60 days or more, and 20 days, respectively, but there were no significant differences in emergence number among treatments when refrigerated for different days. It indicated that age and refrigerating time could influence the process of development at lower temperature and emergence after refrigeration of T. ostriniae. The viability was higher when refrigerated at early stage or in a short period. Therefore, the effects of age and refrigerating time need to be considered for improving T. ostriniae cold-tolerant performance in mass production.