Abstract: When etiolated seedlings of wheat were exposed to light, their leaves would be greening and aparent photosynthesis increased; the activity of Rubis CO(Ribulose-1,5-Bisphopate Carboxy-lase-Oxygenase)decreased at first and increased after continuous illumination for 12 h. We had also studied the structure changes of lamella in the top and base leaves which received a continuous illu-mination for 24 h and 48 h and measured their photochemical activities at the same time. The results showed: at the begining, PSⅠ activity was very high, as the lamella got a raise in number, PSⅠactivity decreased while PSⅡ increased. It suggested that the chlorplasts were developed and im-proved in their structure and function during the process of greening of etiolated wheat seedlings,thus the two photosynthetic systems were equvialently distributed, the utilizing efficiency of light energy by chloroplasts was increased.