Abstract: Rice ( Var: 6536) Was exposed to acute and chronic dose of hydrogen fluoride ( HF ) in open-top field chambers. The results indicate that there is a linear inter relationship between the fumigation period and the concentration of HF causing injury to 5 % of the rice foliage. Its regressive equation is InY = 5.42- 0.72 In× (r= - 0.9929, p<0.001). So, we can get its threshold curve. According to the dose-accumulation formula, the accumulation coefficient (K) is 2.63 after HF fumigation. The yield of rice will be affected at different degrees when the dose of HF is beyond its injury thresholds.