Objective: The objective is to explore the differences in clinical symptoms, imaging and treatment between childhood acute lymphoblastic leukemia (ALL) combined with Pneumocystis pneumonia (PCP) and AIDS combined with PCP. Methods: A retrospective analysis of childhood ALL diagnosed with PCP in our hospital from 2015 to the present, was compared with literature searched by “艾滋病/AIDS” and “卡氏肺孢子虫肺炎/Pneumocystis pneumonia” as keywords from CNKI database, Wanfang Resource database, PubMed database and Science Online database, to find out the differences in clinical symptoms, imaging manifestations and treatment of the two types of patients. Results: Two patients in our hospital were diagnosed with ALL combined with PCP, and the remaining suspected patients were cured after empirical treatment. Both patients had fever with dry cough and shortness of breath of onset, a few moist rales over lung fields and oxygen saturation decreased. Both could maintain the normal arterial oxygen with the help of non-invasive ventilation. Lactate dehydrogenase (LDH) didn’t increase significantly. Both HRCT showed patchy opacities, one case had consolidation, and the other had scattered nodules. Patients underwent fiberoptic bron-choscopies and bronchoalveolar lavage, high-throughput examination confirmed the diagnosis of PCP, and both improved after the treatment with caspofungin, TMP-SMZ, and glucocorticoids. Conclusion: The clinical symptoms, imaging manifestations and treatment of ALL combined with PCP and AIDS combined with PCP are similar, but LDH does not increase significantly at the onset of ALL combined with PCP, and positive lung signs are more common than AIDS combined with PCP.