Abstract: OBJECTIV To explore the chest CT features of the children with Mycoplasma pneumoniae pneumonia and children with M. pneumoniae pneumonia complicated with Streptococcus infection and analyze the value in differential diagnosis so as to provide guidance for clinical diagnosis and treatment of the disease. METHODS A total of 74 children with pneumonia who were treated in the hospital from Nov 2013 to Nov 2015 were enrolled in the study. According to the results of detection of serum MP-IgM and blood culture of Streptococcus, 32 children with single M.pneumoniae pneumonia were assigned as the group A, and 42 children with M.pneumoniae pneumonia complicated with Streptococcus infection were set as the group B. The rates of emergence of signs of airway and pulmonary interstitial lesions in the chest CT examination were compared between the two groups of children, the pleural effusion volume and the volume of enlarged lymph nodes were compared between the two groups of children, and the morphological features of lung lesions were observed and compared between the two groups of children. RESULTS The chest CT examination showed that the proportions of the children with ground glass opacities, reticulation, thickening of bronchial wall, and thickening of bronchovascular bundles were significantly higher in the group A than in the group B (P<0.05). The proportion of the children with pleural effusion was 57.14% (24 cases) in the group B, significantly higher than that in the group A (P＜0.05). The thickness of pleural effusion of the group B was (14.63±12.57)mm, significantly greater than that of the group A (P＜0.05); the maximum transverse diameter of enlarged lymph nodes of the group was (11.29±3.26)mm, significantly greater than that of the group A (P＜0.05). As compared with the morphological feature of the lung lesions, the proportion of the children with fan-shaped sheet shadow was 75.00% (24 cases) in the group A, significantly higher than that in the group B (P＜0.05); the proportion of the children with irregular pulmonary real opacities was 88.10% (37 cases) in the group B, significantly higher than that in the group A (P＜0.05). CONCLUSION The change of signs of pulmonary interstitial lesions is dominant among the chest CT imaging features of the children with single M.pneumoniae pneumonia; when it is complicated with Streptococcus infection, the CT imaging shows the lung patchy shadows due to alveolar inflammation, with the pleural effusion and enlargement of lymph nodes more obvious.