Objective：To analyze the clinical characteristics，peripheral blood cells and chest CT of family aggregated Mycoplasma pneumonia（MP） pneumonia and family-aggregated coronavirus disease 2019（COVID-19）. Methods：The clinical manifestations，peripheral blood cells and CT results of family-aggregated MP pneumonia and family-aggregated COVID-19 were compared to comprehend the similarities and differences. Results：MP pneumonia tended to occur in the younger age group，with main manifestations of dry cough and fever，often accompanied by pharyngalgia. Chest CT showed that the pneumonia was extended the lung field from the hilum to the outside，involved multiple lobes and easily consolidated. However，COVID-19 tended to occur in the older age group. Patients with underlying diseases were more likely to have complications and fever was the main manifestation，often accompanying dry cough，depression，chest pain and chest tightness. Chest CT showed that it mainly involved the peripheral lung and ground glass opacities. WBC，absolute lymphocyte，absolute neutrophil，Hb，PLT and CRP between two groups（all P values were greater than 0.05） had no significant differences；digestive tract symptoms were relatively rare；weakness was going to accompanied with all symptoms. Conclusion：There are many similarities between family-aggregated MP pneumonia and family-aggregated COVID-19 in the clinical，peripheral blood cells and imaging manifestations，which are easy to be misdiagnosed，and early etiological examination is helpful for early diagnosis.