The invention discloses a preparation method of composite CNTs (Carbon Nanotubes) with nano SiC generated in situ on surfaces. The preparation method comprises the following steps of, through synchronous ultrasonic dispersion and mechanical agitation, uniformly adhering nano silica fume in a specific proportion to the surfaces of the CNTs in a PVP (Polyvinylpyrrolidone) ethanol solution, and afterwards, generating a layer of SiC with a nano-scale thickness on the surfaces of the CNTs through an in-situ reaction, so as to form a SiC/CNTs composite material with a bud-stem or shell-core structure. The SiC/CNTs material prepared by the method provided by the invention does not destroy the structures of the CNTs; further, the dispersion uniformity of the CNTs and the SiC can be guaranteed; thedirect contact among the CNTs and a matrix is to be reduced in a matrix material; interface reactions among the CNTs and the matrix are regulated and controlled; the interface bonding among the CNTsand the matrix is enhanced, and the favorable electric conduction and heat conduction and the high ductility of the matrix are reserved while the mechanical performance of a metallic matrix is improved.