The present invention provides a breeding method for tetraploid ricinus communis. The method comprises: collecting a ricinus communis germplasm resource, performing morphologic character analysis and chromosome ploidy identification, selecting good diploid varieties, carrying out mutagenesis by using colchicine and oryzalin; performing chromosome ploidy identification on F1 generation seeds, selecting homozygous tetraploids, and performing economic character analysis and identification on the F2 generation, so as to breed good tetraploid ricinus communis.