New energy plant duckweed was used as material, we studied the effects of five different concentration of IAA at 0.001, 0.01, 0.1, 1 and 10 μmol/L (0 μmol/L as control) on the growth and starch accumulation of duckweed. The results showed that: （1）Low concentrations (0.001, 0.01 and 0.1 μmol/L) of IAA could effectively promote the chlorophyll content, net photosynthetic rate and biomass yield of duckweed, which significantly increased by 14.7%, 10.6%, and 28.1% compared with the control group at the concentration of 0.001 μmol/L IAA. （2） High concentrations (1 and 10 μmol/L) of IAA can regulate the starch accumulation and increase the activity of AGPase (ADPglucose pyrophosphorylase), a key enzyme in starch synthesis. As compared to the control, the starch content and AGPase activity were significantly increased by 35.0% and 14.1% at 10 μmol/L IAA treatment, respectively. These results suggest that low concentration of IAA treatment can effectively promote the biosynthesis of chlorophyll and photosynthesis of duckweed, which is conductive to the accumulation of biomass, and high concentration of IAA can promote the starch percentage and total starch accumulation by enhancing the activity of AGPase.