The invention relates to a weighted water-based drilling fluid realizing low damage particle size gradation and used for drilling of reservoirs of high-temperature ultra-deep wells and is applicable to drilling of long horizontal sections of shale with microfractures. According to the technical scheme, the drilling fluid is prepared from raw materials as follows: 13.5-15 g of bentonite, 0.675-0.75 g of sodium carbonate, 4.5-5 g of calcium oxide, 2.7-3 g of a sand carrying agent, 45-50 g of sulfonated phenolic resin, 45-50 g of sulfonated lignite resin, 45-50 g of sulfonated lignite, vanadium-titanium-iron ore powder and nanometer barite for adjusting the density to 2.50 g/cm <3>, 27-30 g of a lubricant, 27-30 g of a non-permeable borehole stabilizer, 27-30 g of nano-calcium carbonate, 18-20 g of an anti-rust agent and 900-1000 g of tap water. Clay base slurry is prepared, then calcium oxide is added during stirring at the speed of 500 r/min, the treatment agents are added in sequence after continuous stirring, the density of the system is adjusted to 2.5 g/cm<3>, and the weighted water-based drilling fluid realizing low damage particle size gradation is prepared finally. The drilling fluid system contains few solids, has low damage to the reservoirs, has good rheological property and low filtration loss in a high-temperature deep well and is used for development of the reservoirs of high-temperature ultra-deep wells.