Acute respiratory failure with diffuse pulmonary infiltration was occurred in a patient with malignant lymphoma 1month after the 8th CHOP chemotherapy. The ground glass and consolidation appearances on chest C-T in this immunodeficient patient could be presented in many clinical situations such as pneumonia by opportunistic infections(fungal, parasites, viral, and usual bacterial pathogens), anti-tumor drug's pulmonary toxicity and tumor invasion. And the other diseases of acute interstitial pneumonitis, alveolar proteinosis, BOOP, pulmonary edema and alveolar hemorrhage, which could present the same radiological findings, should included in differential diagnosis. This patient was diagnosed as the opportunistic pneumonia by Pneumocystis carinii and probably Cytomegalovirus through bronchoalveolar lavage and transbronchial lung biopsy.