By the analysis on progeny obtained from different crossing designs in single pistillate castor-oil plants, it is determined that single pistillate character is controlled by nucleus genes. Its genetic way is multiple gene additive effect, and it is possible that inhibitory gene exists. On the basis of genetic feature of pistitlate castor-oil plants, it is put forward how to select and breed synthetic varieties and single pistillate strains and how to use these strains to breed hybrids.