Abstract: This paper reports the research results of effects SO₂ of at low-concentration on productivity of the crops in long-term exposure in the open-top chamber. The results show that0.1mg/m³ SO₂ can reduce yield of rice, wheat corn, soybean, potato. and Chinese Cabbage in long-term exposure. There is a more significant decrease in yield of theexperimental crops at 0.25mg/ m³ SO₂. The SO₂ threshold concentration of reducing yield for the sensitive crops is 0.03-0.05mg/ m³, 0.07mg/ m³ for the moderate sensitive crops, and 0.09-0.17mg/m³ for the resistant crops. The decrease of bearing is a main cause of reducing yield for rice, wheat, corn and saybean. There is nota significant effect on accumulation of dry matter. The reducing yield of the experimental crops don't directly relate to leaf injury.