The invention provides a preparation method of a carbon nanotube composite wire. The preparation method comprises the following steps of: preparing carbon nanotube fiber; constructing an electroplating device, wherein the electroplating device comprises a positive electrode and an electroplating liquid arranged in an electroplating tank; winding the carbon nanotube fiber through an output shaft, contacting the carbon nanotube fiber with a conductive electrode and immersing the carbon nanotube fiber into the electroplating liquid; and using a switched-on pulse power supply to carry out electroplating, and preparing and collecting the carbon nanotube composite wire. Compared with the prior art, the pulse electroplating method is adopted, copper nano-crystal grains are directly and uniformly deposited on the surface of the carbon nanotube fiber and in the intervals among carbon nanotubes, the interface binding force between the carbon nanotubes and copper layers is effectively improved, the interaction among crystal boundaries effectively increases the strength and conductivity of the carbon nanotube composite wire, and by adopting the method, the carbon nanotube composite wire light in weight, high in conductivity and high in strength can be prepared.