In hospital-acquired pneumonia, the most common causative organisms are still Gram-negative bacilli, such as Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, Acinetobacter baumannii, Haemophilus influenzae, etc. Gram-negative bacilli account for about 60% of the total, and drug-resistant bacteria are the most common, making it more difficult to treat. Gram-positive bacteria are not uncommon, often Staphylococcus aureus, which is dominated by methicillin-resistant Staphylococcus aureus, but also Streptococcus pneumoniae, enterococci, coagulase-negative staphylococci, etc. Some patients can have mixed infections, which can be combined with mycoplasma, chlamydia, Legionella, anaerobic infections. Some patients with hospital-acquired pneumonia can sometimes have a combination of Mycobacterium tuberculosis or fungal infections, which can make their condition more complex and severe. Therefore, the anti-infective treatment of hospital-acquired pneumonia should be based on the causative agent as much as possible, and effective anti-infective drugs should be selected.