The invention provides adjustable and controllable TiO2-Au composite water-based nanofluid and a preparation method thereof. Different effects are compounded by adjusting and controlling the volume ratio (1:1-1:20) of a titanium trichloride solution to gold nanofluid with different mass fractions (0.006%-0.05%); when the volume ratio of the titanium trichloride solution to the gold nanofluid with the mass fraction of 0.01% is 1:5 and after reaction is carried out at the temperature of 180DEG C for 24 hours, the formed nanofluid can be stably stored for 15 days; a heat conductivity coefficient of the nanofluid is improved by 48.37% compared with that of water, and is improved by 16.01% and 35.15% respectively compared with those of Au nanofluid and TiO nanofluid with single components. The composite water-based nanofluid prepared with the preparation method provided by the invention has the advantages of high heat conductivity coefficient, good suspension stability and simple process; the application range of the nanofluid in a heat exchange system is widened.