A valve seat has a first valve plate and a second valve plate detachably connected to the first valve plate. The first valve plate has a first trough and at least one pair of first dents, each pair including two first dents capable of respectively forming two first passages with a housing of a pneumatic hammer. The second valve plate has a second trough, at least one pair of second dents, at least one inlet tunnel, and at least two inlet channels. The second trough faces to and communicates with the first trough. Each pair of second dents includes two second dents capable of respectively forming two second passages with the housing. Each inlet tunnel is formed through the second valve plate and communicates with the two second passages. The at least two inlet channels communicate with the second trough and the at least one inlet tunnel.