A novel submodel scheme based onSt.Venant's principle hasbeendeveloped toevaluate thereliability Thermal Cycle Test(TCT)forCMOS ImageSensor (CIS). Theregion of interested inboard level CISpackage islead-free paste, which isthepeakstressed areatopredict fatigue life. A solid finite element modelofCISusing ANSYS codesisdeveloped to predict thethermal strain distributions. Thepredicted thermal-induced displacements werefoundtobeverygood agreement withtheMoireinterferometer experimental inplane uandv deformations. Thedeveloped finite element modelisthenapplied toinvestigate thereliability ofthe JEDECstandard JESD22-A104 TCT. Inordertosave computational timeandproduce satisfactory results inthe coarse region ofinterest, anindependent morefinely meshed so-called submodelschemebasedon cut-boundary displacement methodisgenerated. Themeshdensity for different arearatio ofsubmodel/global modelwasverified andtheresults werefoundtobegoodagreement with previous researches. Themodified Coffin-Manson equation isapplied toevaluate thepredicted fatigue life ofSnAgCu pastes. A series ofcomprehensive parametric studies were conducted inthis paper.