To provide a method for preparating a hydrate slurry which can prevent from increase and fluctuation of pump power and from blockade of a heat exchanger caused by the supercooling when hydrate formation, by forming directly the secondary hydrate from the aqueous solution.

The method for the preparating a hydrate slurry used as a cold transporting medium, by cooling an aqueous solution of a guest compound to form the primary hydrate or the secondary hydrate is provided. By making an initial concentration of the aqueous solution in 10 wt.% or less and by cooling while maintaining the concentration of the hydrate slurry mother liquid in 10 wt.% or less, the secondary hydrate is directly prepared from the aqueous solution.