Farmland soils are the important source of greenhouse gases emissions, so it plays an important role for slowdown of the climate change by reducing the emissions of greenhouse gases from farmland soils. Because of high carbon content and carbon stability of biochar, and its influence on regulation of soil structure and microorganism, biochar has the important effect on increasing of soil carbon accumulation and reducing of the greenhouse emissions. However, biochar is setting up with high or low addition amount currently, possess a big blind area, and few reports are involved in effecting of biochar on reducing effectiveness of comprehensive greenhouse. Simulation experiment indoor of soil column was conducted in this experiment, and adding 0%(0 t/hm²), 0.5%(5 t/hm²), 2%(20 t/hm²), 4%(40 t/hm²), 6%(60 t/hm²), 8%(80 t/hm²) biochar (the biochar was prepared by pyrolyzing corn straw at 500-550 ℃ under oxygen limited condition) into red dryland land of Southern China under urea application condition (300 kg/hm²), and using static chamber/gas chromatograph techniques to collect and determine the CO₂, CH₄, N₂O fluxes. The results showed that CO₂ emission was significantly increased by biochar application during simulation experiment indoor of soil column, and the relationship between addition amount of biochar and emission amount of CO₂ meet the linear equation: y=12.591x+235.02(R²=0.834, n=24). The CH₄ emission was almost inhibited and the N₂O flux was significantly decreased when biochar addition ratio was above 2% (including 2%), and the comprehensive greenhouse effective of CH₄ and N₂O were significantly decreased, and the decreased range was bigger when the ratio reached 4%. But N₂O emission was significantly accelerated by adding small amount of biochar(0.5%), and no significant effective of reducing the comprehensive greenhouse. The apparent decomposition rate of biochar decreased as the increasing of biochar addition, indicating that the higher biochar addition with the more carbon accumulated in soil. As a conclusion, recommended applying amount of biochar is 20 t/hm² in agricultural production, which has a better effect both on carbon fixation and reduction.