Abstract: A boiler for a steam mop includes a boiler, one end of which is disposed with a water inlet and a steam outlet, the body is disposed with a loop liquid way and a heating device to vaporize the water inside the liquid way; a water inlet pipe, connected to the water inlet of the boiler through a first pipe joint; a steam pipe, connected to the steam outlet of the boiler through a second pipe joint; a steam nozzle, connected to the other end of the steam pipe. The boiler is applied with a loop liquid way, and the heating element is disposed beside the liquid way, so the water in the liquid way is heated with long heating trip.