The objective of the present work is to study the effects of CO2 injection on the hydromechanical behavior of a fault running across a reservoir in view of safety storage risk assessment. At the fault zone scale, the equivalent permeability of the statistically distributed fractures is modeled by singular integral equations method. At the site scale, a fault is modeled as a shallow layer of filling material surrounded on both sides by a series of hydromechanical joint elements. The fluid flow across the fault due to the injection is studied. The failure probability on the fault, due to effective stress change can also be estimated by the model.