Abstract: The effect of photoperiod on growth and flowering of Myriophyllum spicatum L. was probed by artificially increasing or decreasing light time. The seedlings were planted on water tanks and divided into four groups and subjected to different photoperiod treatment:( 1) Control: natural photoperiod fromMay to September in Wuhan;( 2) 8h short day treatment;( 3) 16h long day treatment;( 4) 24h full day treatment. It was found that 8h short day photo-period was not favorable to the growth and florence development. The florescence and flower bud formation, flowering time and the germination of seeds under different photoperiod were assessed by stat istical analysis. The results demonstrated that under long term short day, Myriophyllum could not form florescence and fruits. On the contrary, 16h long-day photoperiod could increase the height, promote branching and increase biology mass. But 24h long-day treatment suppressed the growth compared to the natural photo-period condition which is average 13.5h. Under long-day photo-period, the florescence forming and flowering were postulated and the amounts of florescence were also reduced significantly. Interestingly, the seeds produced under long-day photoperiod had a higher germinat ion rate. Our results provided ecological restoration with a new idea for obtaining the high quality seeds.