The effects of different K fertilizer rates on the biomass, the activites of antioxidant enzymes, the MDA content, the chlorophyll content and the contents of vindoline，catharanthine，vinblastine and vincristine of flowering Catharanthus roseus were investigated in greenhouse. The results indicated that the KCl could promote the growth of C. roseus when it was 100 ~ 400 mg/kg. The activities of SOD, CAT and POD enzymes and the content of chlorophyll were gradually increased，but the MDA content was decreased with the increase of KCl concentration. The excess of K nutrition could inhibit the growth of C. roseus when the KCl was 800 mg/kg. The uses of 400 mg/kg KCl could significantly promote the growth and the alkaloids metabolism of flowering C. roseus. Also the vindoline, catharanthine, vinblastine and vincristine contents were highest when the KCl was 400 mg/kg，with 42.81, 37.82, 1.88 and 3.1 mg/g, respectively.