Abstract: It was investigated that the denitration of a simulated high level liquid waste using formic acid at 90 ℃ under different formic acid to nitrate ratio(r). The results show that the denitration efficiency increases with the increase of the formic acid to nitrate ratio, and the amounts of precipitating components after denitration vary with formic acid to nitrate ratio. When the formic acid to nitrate ratio is 1.4, the pH of the solution is the highest after denitration. Thermogravimetric analysis for denitration products suggests that the weight loss decreases from 45% to 35% and the temperature of complete decomposition is between 570 ℃ to 620 ℃ with increasing formic acid to nitrate ratio from 1.0 to 1.6.