Kinetics of natural gas reburning is modeled on the basis of GRI3.0 and the method of Gear. The calculation results indicate that the model agrees with experiments. HCN, NHi and HCCO play an important role in the reburning system. Injecting NH3 and increasing the fraction of HCCO in the reburning system will promote NO reduction. Injecting natural gas at the places wherein the fraction of NO is highest is a benefit to de-NOx. There exists an optimal value of ratio of natural gas: NO for reburning system. The influences of temperature, excess oxygen ratio and pressure are also discussed in the reburning system.