A dryer includes a sealed drum, a heat pump system, a vacuum device and a steam generating device. The steam generating device connects with the interior of the drum to introduce hot steam into the interior of the drum. The vacuum device connects with the interior of the drum. The heat pump system is arranged external to the drum. Heat generated by the heat pump device is exchanged with the outer surface of the drum through a liquid medium so as to heat the wet clothes in the drum. Simultaneously, damp-hot air mixed with the water vapor in pumped from heating clothes in the drum by the vacuum device and the hot steam pumped into the drum and contacted with clothes are cooled and condensed into water. The water produced by damp-hot air is connected with water provided by the steam generating device.