Abstract: The growth, yield and quality of sweet potato were examined by field plot test and physiological test in lab after application of mepiquat chloride SP. The growth of sweet potato retarded but the yield increased after treatment of mepiquat chloride under 150～300 mg/L. The higher the dose, the lesser the growth but the higher the yield. The content of starch and soluble glucose of sweet potato did not vary obviously compared to the control after mepiquat chloride application. It showed that mepiquat chloride has not bad influence to the quality of sweet potato at the tested dose.