The invention discloses an antibacterial and hydrolysis-resistant thermoplastic polyurethane elastomer and a preparation method of the polyurethane elastomer, and belongs to the field of high molecular materials. The polyurethane elastomer is prepared from the following raw materials by mass percentage: 40-70% of hydroxyl-terminated polyhydric alcohol, 20-40% of diisocyanate, 4-15% of micromolecular dihydric alcohol chain extender, 1-5% of hydrolysis stabilizer, 0.1-0.5% of antioxidant, 0.1-0.5% of light stabilizer, 0.1-0.5% of mildewproof agent, 0.5-1% of lubricant and 0.001-0.005% of catalyst. The mildewproof agent is added, so that the antibacterial property of the polyurethane elastomer is improved, and the service life of the polyurethane elastomer is prolonged; the hydrolysis stabilizer is added, so that the problem of degradation of the polyurethane elastomer in a hygrothermal environment is solved; and compared with current commonly used disc method and casting method technologies, a product synthetized by the polyurethane elastomer has the characteristics of stable extrusion, uniform molecular weight and few colloidal crystal point.