The invention relates to a preparation method for a rare earth polymer, and particularly relates to a preparation method for a rare earth polymer which has narrow molecular weight distribution and high Mooney viscosity. The method includes the steps of: under the effects of a homogeneous phase rare earth catalyst and an activator, performing a polymerization reaction to a monomer in an organic inert solvent to prepare the rare earth polymer having narrow molecular weight distribution and high Mooney viscosity, wherein the catalytic system is composed of rare earth carboxylate, alkyl aluminum, a halogen compound, and conjugated diene according to the ratio of 1:5-40:1-4:5-30. By means of the method, the polymer, which is more than 98% in content of cis-1,4-structure, is adjustable in weight-average molecular weight within the range of 100,000-1,500,000, is less than 3 in molecular weight distribution, is higher than 60 in raw rubber Mooney viscosity and is 2.0-5.0 dL/g in solution viscosity ([eta]), can be prepared.