In power plants having no gas source，a feasible option is that re-burning of coal gas produced in powder coal burner to reduce emission of NOx，i.e.in order to the coal gas，using air and water vapor as medium to gasify a part of coal below 1000℃.In this paper GRI3.0 mechanism is selected and after simplifying a multi-step mechanism including 26 species and 63 reactions is got for simulating a 130 t powder coal burner.The design calculation of the inlet and the ratio of re-burning gas are done and a alteration design that can make 80% reduction of NOx is proposed.The results show that the re-burning does not have significant influence on burnout ratio of coal.The inlet of the third air wind should be moved up 3 m to increase the reduction time of NOx.The ratio of re-burning gas should be controlled at 30% to strengthen its reduction performance.