Objective The investigate value of computed tomography (CT) in the differential diagnosis of streptococcus infection pneumonia and mycoplasma infection pneumonia in children. Methods A total of 160 children with pneumonia infected by single pathogens during the period from January 2017 to December 2018 who were admitted to the hospital were selected. And retrospective analysis was conducted. The above subjects were divided into mycoplasma group (100 cases) and streptococcus group (60 cases) according to different types of pneumonia in the patients. All patients underwent CT scan before treatment. The imaging findings of CT were compared between the two groups. Results The white blood cell count of mycoplasma group was significantly lower than that of streptococcus group (P<0.05). The thickness of pleural effusion and thickness of lymph node nodule shadow were significantly smaller than those of streptococcus group (P<0.05). The ground-glass opacity, proportion of people with thickening of centrilobular nodules and diffuse bronchial wall in mycoplasma group were significantly higher than those in streptococcus group (P<0.05). There was no significant difference in chest CT findings such as reticular and linear fuzzy image, pleural effusion, lymphadenectasis or consolidation between the two groups (P> 0.05). The involved rate of more than 1 leaf in mycoplasma group was significantly higher than that in streptococcus group (72.00% vs 43.33%) (P<0.05). There was no significant difference in the involved rate of lung lobes between the two groups (P>0.05). There were significant differences in the morphology of intrapulmonary lesions between the two groups (P<0.05). Conclusion Chest CT is of relatively better differential diagnosis value for streptococcus infection pneumonia and mycoplasma infection pneumonia in children. The two kinds of pneumonia can be differentiated by CT signs such as thickening of pleural effusion thickness, thickening of lymph node nodule shadow, thickening of bronchial wall and centrilobular nodules.