The invention discloses a vacuum drier which comprises a circulating water pump, a solenoid valve and a filter, wherein one end of the circulating water pump is arranged on a circulating water pipeline; a water ring vacuum pump, a fourth roots pump and a third roots pump which are connected by air pipelines sequentially are arranged at the other end of the circulating water pump; the other end of the third roots pump is connected with air outlet ends of a first roots pump and a second roots pump respectively by an air pipeline; air inlet ends of the first roots pump and the second roots pump are connected with the filter by an air inlet pipeline; the solenoid valve is arranged on an air pipeline between the fourth roots pump and the water ring vacuum pump; and the roots pumps, the water ring vacuum pump, the circulating water pump and the solenoid valve are connected with a control cabinet by a cable. The vacuum drier can vacuumize a dried pipe, so that water and air in the pipe are removed; the ice blockage and corrosion probability of the pipe is reduced; the service life of the pipe is prolonged; and the vacuum drier is wide in application scope and good in drying effect.