Seasonal influenza is an acute viral infection caused by influenza virus, which is often prevalent in summer and winter. In contrast to the prevalent focus on winter flu, summer flu is often ignored by epidemiological researchers. However, summer flu should be studied because of the special immune status and the influenza spread mechanism in the hot and humid environment. Moreover, people are more likely to catch a summertime cold upon suddenly entering relatively cool air conditioning from the hot and humid environment. To simulate summer flu, we established a flu animal model under a high temperature and humidity environment during the day with a relatively low temperature at night to investigate the anti-influenza virus effect and mechanism of Xin-Jia-Xiang-Ru-Yin. The results of RT-qPCR verified virus replication, while pathological sections showed inflammation. The expression of the IFN-γ-related regulatory pathway was measured by PCR and immunohistochemistry. We concluded that Xin-Jia-Xiang-Ru-Yin, which combined antiviral therapy and immune modulation effects, might have important therapeutic benefits against summer flu.