The invention discloses copper and niobium reinforced corrosion-resistant austenitic stainless steel and a preparation method thereof. Alloy elements comprise smaller than or equal to 0.03 C, 12.0-15.0 Ni, 16.0-18.0 Cr, 2.0-3.0 Mo, smaller than or equal to 0.53 Nb, 0.2-0.8 Cu, smaller than or equal to 2.0 Mn, smaller than or equal to 1.0 Si, smaller than or equal to 0.035 P, smaller than or equalto 0.030 S, and the balance Fe, wherein 7.73xC<=Nb<=7.73xC+0.3. After alloy smelting, due to thermal deformation cogging and cold deformation, NbC can be sufficiently broken and distributed in a dispersed manner, and due to high temperature solid solution treatment, coarse and large austenite grains are obtained. Under the hydrogen introducing condition, the alloy corroding current in a 0.5 mol/LH2SO4 electrolyte containing 5x10<-6>F<-> at 80 DEG C is 7.4-9.9 muA/cm<2>, compared with 316L stainless steel, the corroding speed is substantially lowered, and the mechanical performance is slightlysuperior to that of the 316L stainless steel.