Abstract: Structure and function of the photosystem of tungoiltree（Vernicia fordii）saplings were determined after the saplings had been subjected to long-term（118 d）fumigation with low concentration（0.857 1 mg·m^-3 SO₂.The results show that the fumigation led to decrease in photochemical quenching,non-photochemical quenching and apparent photosynthetic electron transport rate（ETR）,but to increase in fluorescence output.The results also show that the light conversion efficiency and potential activity of the photosystem Ⅱ（PSⅡ）and photosystem Ⅰ（PSⅠ）decreased with SO₂ fumigation.It can,therefore,be concluded that the long fumigation with low concentration SO₂ resulted in destruction of the structure of PSⅠ and PSⅡ,thus causing decrease in total light conservation efficiency and potential activity of the photosystem.