Abstract: Mechanism study of formation and control of nitric oxide (NO) and nitrous oxide (N₂O) during coal two stage combustion was made on a bench scale circulating fluidized bed (CFB). The experiment results show that: 1) NO emission decreases quickly with the second air ratio rising; when the position of second is higher, NO emission is lower. 2)With the second air ratio rising, N₂O emission distinctly increases until a flex point; then with the second air ratio rising again, N₂O emission decreases quickly; when the position of second air is higher, the rate of N₂O concentration up and down is higher.