The invention discloses a catalyst for preparing 2-ethyl hexanal. The catalyst is prepared from an Al2O3 carrier, a first metal ingredient and a second metal ingredient, wherein the first metal ingredient and the second metal ingredient are loaded on the Al2O3 carrier. The catalyst is characterized in that the first metal ingredient is one or two of Ag, Co and Rh; the second metal ingredient is Pd; through being metered by the total weight of the catalyst, the content of the first metal ingredient is 0.001 to 0.05 weight percent; the content of the second metal ingredient is 0.01 to 1.0 weightpercent. The invention also discloses a preparation method of the catalyst and a preparation method of the 2-ethyl hexanal. The isooctane aldehyde selective hydrogenation can be effectively performed; the treatment quantity of the catalyst is greatly improved; the process flow process is simple; the energy consumption is low; meanwhile, the raw material conversion rate reaches 99 percent; the product selectivity reaches 98.5 percent or higher.