The invention discloses a preparation method of carbon nanotube/ferroferric oxide composite sponge with negative giant magnetoresistance performance. The method comprises the following steps: step 1,preparing a carbon nanotube precursor solution; step 2, preparing a carbon nanotube sponge; 3, preparing a Fe3O4 precursor solution; 4, preparing a carbon nano tube/Fe3O4 composite sponge; step 5, washing the carbon nano tube/Fe3O4 composite sponge graphene belt sponge; and step 6, drying the carbon nanotube/Fe3O4 composite sponge. According to the preparation method, the carbon nanotube sponge isprepared by adopting a chemical vapor deposition method, and Fe3O4 nano-particles grow in the carbon nanotube sponge by virtue of a three-dimensional porous network structure of the carbon nanotube sponge through a polyol method, so that the carbon nanotube/Fe3O4 composite sponge with negative giant magnetoresistance performance is prepared. The giant magnetoresistance performance of the carbon nanotube sponge is greatly improved while the light weight and high conductivity of the carbon nanotube sponge are maintained.