The invention discloses a heating device used for a steam mop. The heating device comprises a shell, a heating body, a water inlet and a steam outlet, the heating body comprises a water incoming passage, a steam outgoing passage and a U-shaped heating pipe, the water incoming passage is positioned on one side of the U-shaped heating pipe, the steam outgoing passage is positioned on the other side of the U-shaped heating pipe, the water inlet and the steam outlet are directly arranged on the heating body, and both the water incoming passage and the water outgoing passage are arranged inside the heating body. Water is sprayed into the water incoming passage through the water inlet above, is quickly vaporized and sprayed out from space below, enters an outer-side heating cavity and enters the steam outgoing passage through a steam incoming hole, steam is heated by high temperature once again, and the steam after being heated enters from the steam incoming hole above the steam outlet and then is sprayed out from space below. By the heating device, heat of the heating body can be utilized fully, steam conversion efficiency is higher, quality is higher, blockage is prevented, and performance of the heating device is improved.