The present invention discloses a polyisoprene preparation method. According to the method, the method is performed in a single horizontal double-shaft self-cleaning mixer, the horizontal double-shaft self-cleaning mixer comprises a housing with a jacket and at least two stirring shaft in the housing and with stirring paddle blades, and the stirring shafts and the stirring paddle blades are hollow structures. The method comprises: introducing a cooling medium into the jacket and the hollow structures, conveying a reaction material containing a rare earth catalyst, a solvent and an isoprene monomer into the housing, and carrying out a solution polymerization reaction to obtain the polyisoprene. With the method of the present invention, the concentration of the isoprene monomer performing the polymerization is improved, the conversion rate of the isoprene monomer is improved, and the quality of the obtained polyisoprene product is good.