The invention relates to a carbon nanotube-CdTe/CdS nanocomposite and a preparation method thereof. The composite material is prepared by covalently loading CdTe/CdS core-shell quantum dots onto the surface of PEI-MWCNTs. The preparation method comprises the following steps of adding CdTe/CdS quantum dots with a core-shell structure and a crosslinking agent into double distilled water, carrying out ultrasonic treatment for 3 hours, then adding PEI-MWCNTs, carrying out ultrasonic reaction for 24 hours and dialyzing to obtain the carbon nanotube-CdTe/CdS nanocomposite MWCNTs-CdTe/CdS. MWCNTs-CdTe/CdS nanocomposite prepared by the method has a good dispersibility in the aqueous phase as well as a relatively high fluorescence intensity and fluorescence stability and can be used as the novel nanometer fluorescent probe in the fields of photoelectric and biological sensors, biological pharmacy and the like.