Abstract: In this paper,by periodical measuring the growth indices of Phalaris arundinacea in whole growing process in Beigu Mountain wetland,including plant length,sheath height,leaves age and biomass,the seasonal growing dynamic of P.arundinacea were studied and provided the theoretical and technical data for the resources exploitation of P.arundinacea.The results showed that the seasonal growing dynamics of above four growing indices were similar,and all appeared "S" curves.Further analysised,the cubic fitting curve was best.The change trend of absolute growth rate and relative growth rate were almost synchrony,and both exhibited monopeaks curve,but there was little difference in time when negative growth rate appeared.The seasonal dynamic of accumulation absolute growth rate and accumulation relative growth rate of growing indices were both "S" curve shaped,and the cubic fitting curves were best also.