The present invention relates to a method for preparing a modification polymerization initiator with a high conversion ratio by minimizing side reactions. According to the method for preparing a modification polymerization initiator, a modification polymerization initiator which may easily initiate polymerization and provide a polymer with a functional group having affinity with a filler, may be prepared. Particularly, by performing the method using a continuous reactor, the production of by-products may be decreased, and as a result, the conversion ratio may be increased and a modification polymerization initiator with high purity may be prepared in a high yield.