The invention provides monolithic catalysts used for oxidizing CO and methanal under ordinary temperature and the preparation method thereof, which belong to the field of environmental engineering. The monolithic catalyst comprises a carrier, a coating, Pt, Pd and addition agent. The preparation method comprises the steps as follows: the carrier is immersed in mixed solution comprising precursor solution of an auxiliary coating and main coating collosol, and then is blown, dried and calcined; then the carrier is immersed in mixed solution comprising chloroplatinic acid solution, chloropalladite acid solution and nitrate solution of the addition agent for more than 4 hours by adopting an isovolumetric immersion method; and finally, reducing agent is added into mixed solution in which the carrier is immersed under the temperature ranging from 45 to 90 DEG C, and then the carrier is taken out, washed through water and dried so as to obtain target products. The monolithic catalyst used for oxidizing CO and methanal under ordinary temperature and the preparation method thereof have the advantages of simple technology, low cost and the like, are easy to control the operation conditions,and are also easy to produce on a large scale. By adopting the Nanometer Pt and Pd catalyst, CO and methanal can be eliminated under the room temperature, thereby having high antitoxic performance, high moisture resistance and stable property.