The present invention relates to a process for preparing catalyst slurry in a catalyst slurry preparation system and supplying catalyst slurry to an ethylene polymerization loop reactor wherein an accurate control of the pressure within said catalyst slurry preparation system is provided. More particularly, the present invention provides a method for preparing a catalyst slurry and supplying said catalyst slurry to an ethylene polymerization loop reactor, said catalyst slurry comprising solid catalyst and a liquid hydrocarbon diluent, wherein said method comprises the steps of: (a) feeding concentrated catalyst slurry to a mixing vessel by means of a feeding device; (b) diluting said concentrated catalyst slurry in a suitable amount of said diluent in a mixing vessel thereby obtaining a diluted catalyst slurry having a concentration suitable for use in an ethylene polymerization reaction; wherein said mixing vessel is provided with at least one pressure regulating unit connected therewith and wherein said pressure regulating unit comprises a pulsation dampener; and (c) transferring said diluted catalyst slurry from said mixing vessel to said ethylene polymerization loop reactor; characterized in that the method comprises the step of maintaining said mixing vessel essentially free of a gaseous phase by regulating the pressure in said mixing vessel using said at least one pressure regulating unit comprising the pulsation dampener.