The invention discloses a gas heater, and belongs to the technical field of heating equipment. The problems that an existing gas heater easily generates unsmooth air flow in the use process, and harmful gas is generated and threatens the life safety are solved. According to the technical scheme, the gas heater comprises a shell, a combustion platform is arranged in the shell, a fire grate, an airinlet pipe and an igniter are arranged on the combustion platform, an air guide pipe communicating with the outdoor position is further included, a cover body is arranged on the combustion platform, and a smoke discharge channel communicating with a combustion cavity and an air inlet channel communicating with a cavity are formed in the air guide pipe. According to the gas heater, when waste gas generated by combustion in the combustion cavity enters the smoke discharge channel, heat is transmitted to the indoor position, the outdoor air enters the cavity through the air inlet channel, and finally enters the combustion cavity to supply oxygen, when the gas amount is increased, the speed, passing through the air inlet channel, of outdoor air is correspondingly increased, oxygen can be supplied in time, the problem that the airflow is not smooth is avoided, and meanwhile, the waste gas is isolated from the indoor position to ensure life safety.