Porous alumina thin membranes containing parallel regular pores of uniform size (nano scale) and normal to substrate surface have been prepared and fabricated. Their fine pore structure has recently made the porous films to be one of the ideal templates for synthesis of nano-structured materials and MEMS (micro-electro-mechanical systems) and separator for separation those small grains from mixed liquid. Unfortunately, the significant macro-mechanical properties of porous alumina thin membrane have not yet been understood clearly. Because the geometry of this kind membrane is multi-scale covered with mm to μm to nm, macro-mechanical behaviors of the porous alumina thin membranes belong to nonlinear mechanics. To measure and calculate those mechanical properties are difficult. Using "temporal speckle pattern interferometry" to measure successfully the large deflection vs perpendicular uniform pressure. Then the mechanical properties of the porous alumina membranes, such as elastic modulus and fracture strength, can be obtained based on plate/shell models and flexile thin membrane model. The results indicate unusual mechanical behavior of it and help us to understand the relations between microstructure and macro mechanical properties.