The invention relates to a preparation method of a chemically crosslinked nanocomposite hydrogel, which comprises the following steps: (1) adding water, hydrophobic monomers and a surfactant into a container, raising the temperature to a certain temperature, adding a water-soluble initiator, carrying out reaction for 1h-2h, adding acetone solution of a polymerizable photoinitiator into a system, completing the adding within 6h, stopping heating, obtaining nano-microspheres with photo-initiation activity and carrying out dialysis on the prepared microspheres in distillated water for 72h; and (2) adding emulsion of the microspheres with the photo-initiation activity in the concentration of 5%-40% after the dialysis of the step (1) into water-soluble monomers for light radiation. The preparation method has the advantages of simpleness, wide sources of raw materials, high polymerization efficiency and fast polymerization speed, and is applicable to industrial production; and the obtained nanocomposite hydrogel has excellent mechanical properties and good stability.