Abstract: The reaction mechanisms of the olefin?based cycles for ethene and propene formation at Br?nsted acid sites (BAS) in H?SAPO?34 and at BAS and Lewis acid sites (LAS) in Zn@H?SAPO?34 were systematically investigated by means of density functional theory (DFT) calculations combined with microkinetic simulations, with the aim of elucidating the influence of Zn2+ modification on the catalytic performance of the methanol?to?olefins (MTO) reaction. The results demonstrate that the selectivity to propene based on the olefin-based cycle catalyzed by H-SAPO-34 is higher than to ethene (consistent with the previous reports). The Zn2+ modification enhances the acidic strength of neighbouring BAS, significantly reducing the overall free energy barriers for both the ethene and propene formation pathways and improving activity. It also decreases the difference in their barriers. At LAS, the overall free energy barrier for ethene formation has been found to be slightly lower than that for propene, indicating a relative selectivity advantage toward ethene; however, both barriers are significantly higher than those at BAS, suggesting that LAS are not the dominant active sites. Further Microkinetic simulations show that BAS remain the main active sites after Zn2+ modification, with total turnover frequencies (TOF) increased by 2~3 orders of magnitude compared to unmodified H?SAPO?34. The propene selectivity advantage is kept and the relative selectivity towards ethene increases with rising temperature. In summary, the enhancement of B-acid strength and the introduction of LAS by Zn2+ modification improve the overall catalytic activity while maintaining the propene selectivity advantage and reducing the selectivity difference between ethene and propene. This work provides theoretical guidance for the rational design of high?performance MTO catalysts.