A preparation method for a low-temperature SCR catalyst for denitrating diesel vehicle exhaust, being characterized in that the method comprises the following steps: Step 1: preprocessing a ZSM-5, BEA or Y type molecular sieve: weighing accurately the molecular sieve; placing it in an oven, ventilating and heating the oven for four hours under the temperature of 90 °C, and decreasing the temperature to room temperature; Step 2: conducting equal-volume impregnation for the first time: detecting a specific pore volume of the material dried in Step 1, adding a molecular sieve powder of Step 1 into a reaction kettle, calculating soluble molysite solid and soluble nantokite solid according to Cu 2+ and Fe 3+ respectively: Cu 2+ accounts for 1-2% of the total mass of the molecular sieve, and Fe 3+ accounts for 1.5-2.5% of the total mass of the molecular sieve, both of Cu 2+ and Fe 3+ are calculated according to their total amount: preparing Cu and Fe into aqueous solution according to the proportion of 2.5-4.5% of the total mass of the molecular sieve, the total volume of the solution = the mass of the molecular sieve ∗ specific pore volume, slowly adding the solution in the form of mist spray, stirring the solution constantly and continuously stirring the solution for one hour after the completion of the spray; then stirring the solution under the temperature of 60°C for one hour, heating it to a temperature of 80°C and continuing to stirring it into fine powder; Step 3: drying to dehydrate: taking out the powder of Step 2, encasing it in a stainless steel disc, calcining it in a ventilated oven under the temperature of 120°C for two hours, removing water absorbed in surface and passing it through a 40 - mesh screen; Step 4: conducting equal-volume impregnation for the second time: adding the obtained molecular sieve of Step 3 into the reaction kettle, and repeating the impregnation steps of Step 2 and Step 3; Step 5: calcining: calcining the powder obtained in Step 4 under the temperature of 550°C for two hours, naturally cooling it down to be under the room temperature and obtaining dark red powder; Step 6: pulping and coating: adding the powder obtained in Step 5 with an adhesive, and preparing it into serous fluid which is coated on a carrier, dried and calcined to prepare the catalyst. Step 1: preprocessing a ZSM-5, BEA or Y type molecular sieve: weighing accurately the molecular sieve; placing it in an oven, ventilating and heating the oven for four hours under the temperature of 90 °C, and decreasing the temperature to room temperature; Step 2: conducting equal-volume impregnation for the first time: detecting a specific pore volume of the material dried in Step 1, adding a molecular sieve powder of Step 1 into a reaction kettle, calculating soluble molysite solid and soluble nantokite solid according to Cu 2+ and Fe 3+ respectively: Cu 2+ accounts for 1-2% of the total mass of the molecular sieve, and Fe 3+ accounts for 1.5-2.5% of the total mass of the molecular sieve, both of Cu 2+ and Fe 3+ are calculated according to their total amount: preparing Cu and Fe into aqueous solution according to the proportion of 2.5-4.5% of the total mass of the molecular sieve, the total volume of the solution = the mass of the molecular sieve ∗ specific pore volume, slowly adding the solution in the form of mist spray, stirring the solution constantly and continuously stirring the solution for one hour after the completion of the spray; then stirring the solution under the temperature of 60°C for one hour, heating it to a temperature of 80°C and continuing to stirring it into fine powder; Step 3: drying to dehydrate: taking out the powder of Step 2, encasing it in a stainless steel disc, calcining it in a ventilated oven under the temperature of 120°C for two hours, removing water absorbed in surface and passing it through a 40 - mesh screen; Step 4: conducting equal-volume impregnation for the second time: adding the obtained molecular sieve of Step 3 into the reaction kettle, and repeating the impregnation steps of Step 2 and Step 3; Step 5: calcining: calcining the powder obtained in Step 4 under the temperature of 550°C for two hours, naturally cooling it down to be under the room temperature and obtaining dark red powder; Step 6: pulping and coating: adding the powder obtained in Step 5 with an adhesive, and preparing it into serous fluid which is coated on a carrier, dried and calcined to prepare the catalyst.