During the early stages of the pandemic, some coronavirus disease (COVID-19) patients were misdiagnosed as having influenza, which aroused the concern that some deaths attributed to influenza were actually COVID-19-related. However, little is known about whether coinfection with influenza contributes to severity of COVID-19 pneumonia, and the optimal therapeutic strategy for these patients. We retrospectively studied 128 hospitalized patients with COVID-19 pneumonia. All patients were positive severe acute respiratory syndrome coronavirus 2 positive by nucleic acid detection. Sixty-four cases were coinfected with influenza A/B and the other 64 were influenza negative, matched by age, sex, and days from onset of symptoms. Among the 64 coinfected patients, 54 (84.4%) were coinfected with influenza A, and 10 (15.6%) with influenza B. The median duration of viral shedding time from admission was longer for patients with influenza coinfection (17.0 days) than for those without influenza coinfection (12.0 days) (P < .001). The multivariable Cox proportional hazards model showed that the hazards ratio of resolution in lung involvement was 1.878 (P = .020) for patients administered lopinavir/ritonavir, compared with those not administered lopinavir/ritonavir (95% confidence interval: 1.103-3.196). Among influenza coinfected patients, those treated with lopinavir/ritonavir exhibited faster pneumonia resolution within 2 weeks after symptom onset (37% vs 1%;P = .001). There was no difference in lung involvement between influenza coinfected and noninfected groups. Lopinavir/ritonavir eliminated the difference of lung involvement between influenza coinfected and noninfected groups, indicating that lopinavir/ritonavir is associated with pneumonia resolution in COVID-19.