Abstract: The present disclosure relates to a class of JAK inhibitor compounds for treating severe pneumonia. Specifically, the present disclosure discloses a method for treating severe pneumonia, the method comprising administering to a patient in need thereof a therapeutically effective amount of a compound represented by formula (G), isotopically labeled compound thereof, or optical isomer thereof, geometric isomer thereof, a tautomer thereof or a mixture of various isomers, or a pharmaceutically acceptable salt thereof, or a prodrug thereof, or a metabolite thereof.