Three dimensional parametric finite element analysis models were created for typical high density BGA (Ball Grid Array) package to analyze the structure deformation and stress when loading steady temperature upon packages with different sizes. A simplified model for series analysis including equivalent beam and critical solder ball was established to analyze the effect of design parameters upon the mechanical properties of the package. The numerical results reflected the stress distribution and varying traits of the package, main parameters affecting the deformation and stress were identified. The method developed is convenient and effective. Also it can be applied for analysis of different types of BGA, or can be used for different analysis purpose, and is of certain reference value for the design and optimization of such kind of packages.