The invention discloses an epoxy resin composite insulating material with nonlinear conductivity and a preparation method thereof. The composite insulating material is prepared from sintered nonlinear-conductivity inorganic particles, an epoxy resin substrate and a curing agent, the mass ratio of the sintered nonlinear-conductivity inorganic particles to the epoxy resin substrate is (3-7):10, and the mass ratio of the curing agent to the epoxy resin substrate is 1:(3-4). The epoxy resin composite insulating material with the nonlinear conductivity disclosed in the invention is obtained by adding a certain content of the nonlinear-conductivity sintered inorganic particles such as sintered silicon carbide and sintered zinc oxide to the epoxy resin substrate, and the conductivity is very low when electric field strength is low, however, when the electric field strength increases to a certain degree, the conductivity sharply increases; and the epoxy resin composite insulating material with the nonlinear conductivity disclosed in the invention has high application value in special occasions, such as the composite insulating material can be used to allow electric field distribution to be uniform, reduce partial discharge and the like.