Objective To analyse the microcosmic structure of small-diameter PU vascular graft and explore the influence by the wall thickness of vascular graft on its porous properties and tensile stress.M ethods The small- diameter vascular graft with microporous structure was prepared by casting polyurethane (PU) film onto the glass rod model. The microporous structure was charactered by SEM. According to ISO [7198], the testing equipment for such PU vascular graft was designed to test its porous property. The tensile stress was also investigated at INSTRON tensile strength tester (model: 5566). Results The inner surface, the outer surface and the crossing section of this small- diameter PU vascular graft all presented uniformly microporous structure, and the size of micro hole was under 100μ m. Additionally, the porous properties of this vascular graft would reduce with its wall thickness increased, while the tensile stress would increase first and then reduce. All the testing values gained were similar with the results of the same studies made in the world. Conclusions This kind of small-diameter vascular graft made with PU could basically satisfy the needs of implant vascular graft in biomechanics properties.