Through field experiment,effect of 5% Prohexadione Calcium 5% Effervescent Tablets,a plant growth regulator,was explored.Its effect on rice key growing period,plant height,internodes length,resistance to lodging and yield was analyzed.The results showed that spraying 5% Prohexadione Calcium Effervescent Tablets 10 days earlier than rice elongation could effectively reduce plant height,shorten basal internodes length,reduce lodging,increase spike number and grain weight,and then increase yield.The suitable dosage was 12～30 g/667m².