The invention discloses silicon rubber with excellent compressive stress relaxation performance and a preparing method thereof. The silicon rubber is prepared from, by mass, 100 parts of methyl vinylsilicone rubber, 20-40 parts of vapor-phased white carbon black, 5-20 parts of nanometer-modified calcium carbonate, 3-6 parts of hydroxyl silicone oil, 1-3 parts of methylphenyl silicone resin, 1 part of dicumyl peroxide and 0.5-1 part of stearic acid. According to the silicon rubber with excellent compressive stress relaxation performance, the use amount of the white carbon black is lowered, thenanometer-modified calcium carbonate and the white carbon black are matched to serve as a filler, the compressive stress relaxation performance of the silicon rubber is improved, the tensile strengthof the silicon rubber is improved, and the production cost is reduced. The preparing method is simple and high in operability. The silicon rubber with excellent compressive stress relaxation performance can be applied to sealing gaskets of fuel cells, particularly sealing gaskets for the fuel cells of new-energy vehicles.