Abstract： The guideline for diagnosis and treatment of adult community-acquired pneumonia (CAP) (2007 edition) jointly formulated by the Infectious Diseases Society of America ( IDSA) and the American Thoracic Society ( ATS) has a great impact on the clinical management for CAP in China.In October 2019, the two societies revised and updated the guide again.Compared with the 2007 guideline, the new guideline is more concise ; some contents were deleted and some contents have been updated.The main updated points are obvious changes in the compiling mode , the reduced recommendation intensity for macrolides in CAP treatment ,and more emphasizing the relevance of diagnosis and treatment activities to the clinical practice.