The utility model relates to a portable chemical foam extinguisher powered by a gasoline engine, and belongs to the technical field of fire-fighting equipment. The forest fire extinguisher disclosed by the utility model solves the problems of single fire extinguishing mode and easiness in after-combustion of the existing forest fire extinguisher. The device comprises a shell, a gasoline engine is arranged at the bottom of the shell, the power output end of the gasoline engine is connected with a water pump, the water pump is connected with a water tank through a water inlet pipe, the water tank is fixedly arranged on the upper portion of the shell and connected with a spray gun through a water outlet pipe, and a foam liquid tank is arranged outside the water tank and connected with the water tank through a liquid outlet valve and a foam liquid pipe.