The invention belongs to the technical field of alloy materials and discloses an in-situ synthesis nano Al2O3 and toughened WC-Ni3Al composite material and a preparation method thereof. The preparation method comprises the following steps: preparing Ni, Al, Cr, Mo, Zr and B powder according to the mass ratio and putting the powder in a ball mill for dry ball-milling to prepare Ni3Al intermetallic compound powder; putting the Ni3Al intermetallic compound powder and WC powder in solvent for wet ball-milling to prepare mixed slurry, drying the mixed slurry until the residual volume of the solvent being equal to or less than 1%, pulverizing and sieving the dried slurry to obtain mixed powder with the particle size being equal to or less than 250 mum; and sintering the mixed powder by adopting the spark plasma sintering technology to obtain the product. According to the invention, the in-situ synthesis method is adopted to introduce nano Al2O3 in a WC substrate, and Ni3Al intermetallic compound is adopted to replace Co so as to toughen and enhance the WC composite material, so that the in-situ synthesis nano Al2O3 and toughened WC-Ni3Al composite material has the characteristics of low cost and excellent mechanical property.