The invention discloses a preparation method of a carbon nanotube modified organic silicon resin based composite material. The preparation method comprises the following steps: (1) dispersing carbon nanotubes by using a solvent at first, then wrapping a layer of surfactant, and then heating to volatilize the solvent so as to obtain uniformly-dispersed dry carbon nanotubes; (2) diluting organic silicon resin by using an organic solvent until the solid content is 50%, adding the carbon nanotubes treated in the step (1), and uniformly dispersing the carbon nanotubes into the diluted organic silicon resin by adopting ultrasonic dispersion; and (3) removing the excessive organic solvent, and heating for curing to obtain the composite material. According to the preparation method disclosed by the invention, the carbon nanotubes with excellent performance are used as a filler, so that the final composite material is good in electric conductivity. The preparation method disclosed by the invention can reach the best dispersion effect; equipment required by the preparation process is relatively low in cost, the operation is convenient, and the preparation cycle is relatively short; and the used raw materials are nondestructive to structures of a matrix and the carbon nanotubes, so that the preparation method is suitable for industrial batch production.