The present invention relates to a method for producing a modified polymerization initiator, and more particularly, to a method for preparing a modified polymerization initiator, wherein the method includes the steps of: (S1) introducing a first fluid and a second fluid into a reactor, and reacting the compounds included in the fluids, and (S2) obtaining the modified polymerization initiator prepared by the reaction of the step (S1) through an outlet of the reactor, wherein the step (S1) and step (S2) are continuously performed, wherein in the step (S1), the flow amount of the first fluid and the second fluid is maintained constant at the time when the first fluid and the second fluid are mixed, and the flow rate of the first fluid is increased. Also, the present invention provides an apparatus for producing a modified polymerization initiator for performing the same.