The invention relates to an alpha-diimine rare-earth metal catalyst and a preparation method and application thereof, which belong to the technical field of the catalyst. The structural formula of the catalyst is that the preparation method comprises the steps of adding oxaldehyde and methyl alcohol into a reactor, then dropwise adding substituted arylamine into the reactor, dropwise adding toluene solution of LnR3 into the reactor, and after the reaction is completed, removing toluene and carrying out normal hexane recrystallization to obtain the alpha-diimine rare-earth metal catalyst; and the application process comprises the steps of in a glove box or under the protection of the nitrogen, adding the alpha-diimine rare-earth metal catalyst, a cocatalyst, olefin and anhydrous anaerobic toluene into the reactor, terminating the reaction by using alcohol and then drying to obtain polymer. The catalyst of the invention is the non-metallocene rare-earth metal organic catalyst. The method of the invention has the advantages of simpleness and low cost. The catalyst of the invention plays a role in catalyzing when being applied to the polymerization of conjugated diene.