To provide a desalination treatment method of carbide which can considerably reduce the amount of water to be used for washing while lowering the concentration of chlorine in the carbide to a required extent, and a desalination treatment installation.

The method comprises a primary washing step of washing carbide by mixing it with primary washing water and agitating within an agitating tank 2, a primary dehydrating step of separating the primary carbide into a primary dechlorinated carbide and a primary filtrate by a dehydrating machine 3, a secondary washing step of washing the primary dechlorinated carbide in a state to be kept in the dehydrating machine 3 with secondary washing water of fresh water, and a secondary dehydrating step of separating the carbide washed in the secondary washing step into a secondary dechlorinated carbide and a secondary filtrate in the dehydrating machine 3, wherein the secondary filtrate is reused as the primary washing water.