It can be seen from Table 3 that when the zinc concentration is less than 200μmol/L, the SOD content in Dendrobium nobile leaves gradually increases with the increase of zinc treatment time. When the zinc concentration is more than 400 μmol/L, the content of SOD decreases with the increase of zinc concentration. The results showed that the stimulation of low zinc concentration on Dendrobium nobile could promote the synthesis of SOD, which could eliminate the free radicals produced by stress. When zinc concentration is high, no more antioxidant enzymes will be produced, which will lead to more free radicals accumulation in Dendrobium nobile .