The invention relates to an insertion assembly method for an inner stator and an outer stator of a large generator. The method is characterized by comprising the following steps of: horizontally arranging and fixing the outer stator, horizontally slowly pulling the inner stator to make the inner stator slowly slide into the outer stator, lifting the inner stator to a required assembly position byusing a jack after the inner stator is assembled in place in an insertion way, and welding and fixing a spring plate on the inner stator and a corresponding support structure of the outer stator to finish the whole insertion assembly process. The insertion assembly method provided by the invention is unconstrained by the highest bearing capacity of an insertion assembly tool; a special tool used for insertion assembly is simple; the circumference, concentricity and the like of the inner and outer stators are not required to be corrected and adjusted in the insertion assembly; the insertion assembly process is simple, easy and highly operable; and after the insertion assembly is finished, the whole stator is not required to be turned over.