Disclosed is a method for preparing a carbon nanomaterial/polymer composite. More particularly, it relates to an improved method for preparing a carbon nanomaterial/polymer composite capable of solving a dust problem of a carbon nanomaterial powder and a layer separation problem due to large density difference between the carbon nanomaterial powder and a polymer pellet and providing superior physical properties of the composite, whereby an additive used to prepare the carbon nanomaterial/polymer composite is mixed with the carbon nanomaterial powder and prepared into a pellet, which is then mixed with the polymer pellet.