The influence of in situ deSO(x) process on N2O emission in CFB boiler was studied using density functional theory calculations. The competitive adsorption of SO2 and N2O on pure CaO (1 0 0) surface was first studied and the reaction priority was determined. Results showed that SO2 was more likely to adsorb on CaO (1 0 0) surface O anion site, which hindered the catalytic decomposition of N2O on CaO (1 0 0) surface and sulfurized the CaO (1 0 0) surface under reducing atmosphere. Then a partially sulfurized CaO (1 0 0) surface was established to study the catalytic activity of deSO(x) reaction intermediate on N2O decomposition. The O atom transfer process and the surface recovery process were two key steps for N2O decomposition and the rate-determining step was the latter one. The sulfurization of the surface could deactivate its catalytic activity on N2O decomposition compared with pure CaO (1 0 0) surface but it was still better than that of pure CaS (1 0 0) surface. The free Gibbs energy was calculated to incorporate the temperature dependence of respective reactions. When temperature was higher than 373 K, the surface recovery was more likely to proceed via the LH route. (C) 2015 Elsevier B.V. All rights reserved.