The invention concerns a process for preparing a hydrotreatment catalyst, comprising the following steps: a) at least one step for impregnation of a calcined and/or dried catalytic precursor containing at least one element from group VIII and/or at least one element from group VIB and an amorphous support, using an impregnation solution constituted by at least one phosphorus-containing compound in solution in at least one polar solvent with a dielectric constant of more than 20; b) a step for maturing said impregnated catalytic precursor from step a); c) a step for drying, without a subsequent calcining step, said catalytic precursor from step b).