Gas migration poses significant challenges in the petroleum industry, leading to annular pressure and uncontrolled oil/gas leakage, which can dramatically decrease oil and gas production. Despite extensive research efforts, gas migration remains a formidable issue primarily stemming from debonding at the cement sheath-formation interface. In this paper, a hydro-mechanical model aimed at simulating gas migration within the annular space between cement sheath and formation is established. The coupled pore pressure cohesive zone method is used for characterizing gas migration along the cement sheath-formation interface. Gas is derived from the thin formation and the initial stress of cement is set. Leveraging the finite element method, the hydro-mechanical coupling equation is solved. The occurrence conditions of gas migration are investigated, and the effect of cement elastic moduli, formation elastic moduli and formation pore pressure (gas pressure) are unveiled. The method proposed presents a useful step towards prediction of loss of well integrity due to gas migration and provides improved guidance for cement selection and injection optimization.