Infectious lesions of the left lung are defined as pulmonary imaging changes in the left lung, including the upper and lower left lungs, due to infection with pathogenic bacteria. These imaging changes appear as lamellar, large, or patchy blurred shadows with bronchial inflation signs, and are a common manifestation of the inflammatory response of the lung tissue. In layman’s terms, infectious lesions of the left lung are inflammatory changes of the lung caused by infection with various pathogens, including infection with bacteria, viruses, fungi, mycoplasma, and chlamydia, and are a type of pneumonia. Infectious lesions of the left lung require anti-infective treatment, that is, the selection of the appropriate antibacterial drugs, including the use of various antibiotics and antifungal drugs, under the specific type of infectious pathogens.