Objective To explore the cellular immune function and CT imaging features of patients with acquired immune deficiency syndrome (AIDS) and pneumocystis pneumonia (PCP). Methods The clinical data of 53 patients with AIDS and PCP were analyzed retrospectively. According to the clinical stages, they were divided into early-middle stage group (n=23) and late stage group (n=30). The differences of cellular immune function and CT imaging findings were analyzed in the two groups. Results The levels of CD3 + , CD4 + , CD4 + /CD8 + and NK cells in early-middle stage group were significantly higher than those in late stage group (P<0.05). Among the common signs of CT images in the two groups, there were no statistically significant differences in the occurrence frequencies of ground-glass opacity, patchy shadow, mesh nodule shadow and interlobular septal thickening, between-groups (P>0.05). The occurrence frequencies of fiber cord blocklike shadow and balloon or cavity signs in early-middle stage group were significantly lower than those in late stage group, and the occurrence frequency of lunar arch sign was significantly higher than that in late stage group (P<0.05). Conclusion The immune function of AIDS patients with PCP has a significant deterioration trend. There are certain differences in CT signs under different stages, and they can provide a reliable basis for clinical diagnosis and treatment.