A method for preparing fluorescent spectrum adjustable quantum dot nanocomposite particles in the cross-field of nanotechnology and biomedicine, which involves embedding two or more quantum dots with distinguishable fluorescence colors into silica nanoparticles simultaneously within an oil-in-water type microemulsion system. This results in a fluorescent spectrum adjustable quantum dot nanocomposite particle with a size between 10 to 100 nm. By changing the types and ratios of different fluorescence color quantum dots, the position and intensity of the fluorescence peak of the quantum dot nanocomposite particle can be adjusted. This invention facilitates the arbitrary combination of any fluorescence color quantum dots and allows them to be completely embedded into uniformly sized spherical silica particles smaller than 100 nm, resulting in a vast number of quantum dot nanocomposite particles with different fluorescence characteristics. The quantum dot nanocomposite particles obtained by this invention It can be used as a biological fluorescent probe in various fields of biomedicine.