The invention discloses a preparation method of a nanomaterial modified DMD soft composite. The preparation method comprises the following steps: (1) evenly and fully applying a binder to the surface of a polyester film by use of a reverse scraping method, paving a polyester fiber nonwoven fabric on the surface, fully coated with the binder, of the polyester film and then putting the polyester film with the polyester fiber nonwoven fabric into a press for pressing, and curing the pressed film in a drying oven to obtain a DMD composite; (2) adding a prepared class F epoxy resin glue, nanopowder and a dispersing aid to a disperser for mixing, thereby obtaining the class F epoxy resin glue mixed with the nanopowder; and (3) soaking the DMD composite obtained in the step (1) into the class F epoxy resin glue mixed with the nanopowder, and heating the soaked material to obtain the nanomaterial modified DMD soft composite. According to the preparation method of the nanomaterial modified DMD soft composite, the problems of heat resistance, fast curing of coating, coating thickness and homogeneity of the DMD composite are solved successfully, the tearing strength and the dielectric strength of the material are greatly improved, and corona resistance and the partial discharge resistance of the material are improved.