The growth,development and yield of No.2 new seed watermelon affected by ethephon,mepiquat chloride,paclobutrazol were studied in this paper,it showed that 200 mg/L ethephon,150 mg/L mepiquat chloride and paclobutrazol could made length internode and stem shorten,increased stem width.It was very clear that ethephon made the joint position of the first female flower lowered,the female flowers ratio was increased and so the yield was raised to a certain extent.