To investigate the influence of local defects and damages on the tensile properties of geomembranes, different defects, e. g. , circular hole, horizontal seam, vertical seam and oblique seam, as well as damages of different lengths and depths were considered for HDPE geomembrane specimens of three thicknesses, respectively. Tensile tests were carried out by using an electronic universal tensile apparatus to obtain the major mechanical indexes such as tensile curves, tensile strength and elongation. Furthermore, the influences of different defects and damages on tensile properties were compared and analyzed. The results show that circular, horizontal and oblique defects or damages have significant reduction on the tensile properties of geomembranes, with the horizontal seam having the most significant effect on the whole, circular hole being the second, and oblique seam being the least. The greater the damage degree is, the more significant the attenuation of geomembrane mechanical properties is. The vertical seam along the stretching direction has little effect on the tensile characteristics of geomembranes, which can be basically ignored.