The invention discloses four-graded roller compacted concrete applicable to water conservancy and hydropower engineering and a preparation method. The four-graded roller compacted concrete is prepared from raw materials in parts by weight as follows: 1-5 parts of tin nanoparticles, 8-16 parts of ethylene glycol monobutyl ether, 3-8 parts of polydimethylsiloxane, 47-55 parts of cement, 13-21 parts of a water reducer and 78-86 parts of rubbles, wherein the rubbles comprise extralarge stones, large stones, medium-sized stones and small stones and have the size ranging from 5 mm to 120 mm, and the mass ratio of the extralarge stones to the large stones to the medium-sized stones to the small stones is 4:3:4:1; the water reducer is prepared from ingredients in parts by weight as follows: 16-24 parts of methacrylic acid, 7-15 parts of hydroxyethyl cellulose, 2-6 parts of sodium tetraborate, 5-12 parts of waterborne polyurethane and 0.5-4 parts of linseed oil. The four-graded roller compacted concrete adopts a scientific formula and has remarkable energy-saving and environment-friendly benefits, and the compressive strength, the breaking strength, the impervious grade, the anti-freezing strength and the like are improved.