Abstract: The leakage after CO_2 sequestration is critical inthe evaluation of CO_2 storage period and the stability of the cap-rock.In this paper, the commercial FEM software ABAQUS is used with asecondary developmentto analyze the key factors of CO_2 seepage. Meanwhile the gasVander-Walls equation is applied to the supercritical CO_2 compared to theideal gas equation. A simple theoretical result is obtained and verified ina good agreement with that of simulation. The results show that at least150 000 years are needed until CO_2 escapes completely from ahomogeneous cap-rock with a low permeability; the number storageduration is decreasedsto 10 000 years when there is a high permeability leaky well or fractures,hence, fractures or leaky wells should be consolidated before sequestrationor kept away from project areas.