The reaction mechanism of NBC-1 non_chromium iron based catalyst is studied th rough TPD,TPSR and PSR. It is proved that the adsorption of H2O is chemical on t he surface of the catalyst. While H2 is produced the inertial product O*(σ)t hat will cover the active surfa ce is also produced. It will make the surface of the catalyst inactive; CO i s only in gas phase over the surface of the catalyst but not be adsorbed at the r eaction temperature ,and reacts with O*(σ) to produce CO2*(σ). It makes t he surf ace of the catalyst renewed when CO2*(σ) de_adsorbes from the surface. The c ata lyst doesn't participate the reactions in fact, it only provides “the active po ints" on the surface. The shift reaction is actually such a process that the surface of t he catalyst is repeatedly inactivated and renewed alternatively.