Rice paddy field is an important source of CH₄ and N₂O emissions to the atmosphere. Not only does application of nitrogen fertilizer affect CH₄ and N₂O emissions, but also lead to NH₃ volatilization, NO₂^- and NO₃^- leaching and N loss in the form of N₂O and N₂. The addition of urease inhibitor and nitrification inhibitor decreased N₂O emission considerably by slowing down urea hydrolyzation and inhibiting nitrification and denitrification. However, controversial reports were available on their effects on CH₄ production and emission. HQ and DCD are a pair that has currently attracted more attention in the research of this field. In this paper review is presented on general properties and mechanism of nitrification inhibitor and denitrification inhibitor, application of HQ/DCD in the paddy ecosystem and its effect and problems, and in particular, mechanism of HQ/DCD affecting CH₄ emission, with a view to providing some theoretical bases for reasonable application of HQ/DCD, effective reduction of emission of greenhouse gases and high use efficiency of nitrogen fertilizers in paddy field.