Abstract: Tensile tests were carried out on small tensile specimens of domestic A508-3 steel with different thicknesses at room temperature, and the tensile properties and necking parameters were analyzed. Based on the inverse finite element method, the Gurson-Tvergaard-Needleman (GTN) meso-damage model of small tensile specimens were established according to tensile test. And then the effect and the mechanism of thickness on necking behavior of small tensile specimens were analyzed. The experimental results show that all specimens exhibit elastic deformation, uniform plastic deformation and necking deformation during the tensile tests. Little significant effect of specimen thickness on yield strength, ultra tensile strength and uniform elongation were observed. However, when the thickness of the small tensile specimens decrease from 0.75 mm to 0.30 mm, the non-uniform elongation and total elongation decrease significantly, and the necking angle increases significantly. Additionally, when the thicknesses of the small tensile specimens decrease from 0.50 mm to 0.30 mm, the fracture angles increase obviously. According to the GTN meso-damage model analysis, the parameters used to characterize the cavity nucleation and fusion rate significantly decrease in the 0.30 mm thickness specimen, which indicate that the nucleation and fusion of the cavity become more difficult and the resistance to necking increase in the necking stage. The results of GTN meso-damage model for the necking behavior of the miniature specimens are consistent with the tensile tests.