Abstract: Using oryzalin and EMS (ethyl methane sulfonate) as the agents to do the polyploidy breeding on the Cymbidium Golden Elf ′Sundust′. Rhizomes were treated with oryzalin at concentration of 0, 0.001%, 0.002%, 0.003% for 24, 48 and 72 h. After treatment, rhizomes were inoculated to contain a concentration of EMS 0, 20, 50, 70 mg/L solid medium, cultured 1 month transferred to a new culture differentiation medium to obtain tetraploid plants. After selection and plant stabilization, tetraploid plants were obtained. The results showed the concentration of oryzalin is 0.002% processing 48 h, the concentration of EMS is 50 mg/L culture medium was added, the mutation rate is reached 52%, the mortality rate was only 6%. Tetraploid material in the form of plants shown stronger, leaves thicker and leathery, dark green leaves, twisted; porosity increases significantly; chromosome number of diploid strain was 2n=2x=40, chromosome number of tetraploid strain was 2n=4x=80. The chromosomes number of tetraploid strain was 2 times that of the diploid strain.