The present invention relates to a method for filling a multitube catalytic reactor and to a set of inserts suited to implementing this method.The method of the invention is based on the use of inserts of different types allowing superposed layers of catalysts to be placed in the reaction compartments. The heads of the inserts are visually distinct according to the type of insert, making it possible to avoid filling errors and thus allowing the various layers of catalyst to be filled reliably and simultaneously on a reactor scale.