The invention discloses a method of increasing a vacuum surface flashover voltage of an insulating dielectric material and a modified insulating dielectric material. The method comprises the steps of modifying the surface of a solid insulating dielectric material by adopting ozone, to be specific, putting the to-be-processed solid insulating dielectric material in a sealed cavity, vacuumizing the sealed cavity and then inletting ozone for ozone treatment to obtain the modified insulating dielectric material. The surface conductivity, the surface trap level and the trap density of the insulating dielectric material after the ozone treatment are changed; the surface conductivity is increased obviously, the surface trap level is reduced and the trap density is increased. The method can obviously increase the vacuum alternating current surface flashover voltage of the solid insulating dielectric material; and the method is simple and convenient to operate, has low complexity of the implementation process, relatively good repeatability and strong environmental friendliness, and can be widely applied to the surface treatment of the solid insulating dielectric material in the technical field of high-voltage insulation.