Biaxial tensioning test is made on crossshaped sample of PE geomembrane. The difference between the mechanical performance of PE geomembrane under biaxial tensioning and that under uniaxial tensioning is discussed. The breaking strength and breaking stretching ratio of PE geomembrane in longitudinal direction and transverse direction under biaxial tensioning are measured. The testing data of PE geomembrane under biaxial tensioning are compared with those under uniaxial tensioning. Conclusions drawn are as follows: 1) Under biaxial tensioning, the longitudinal breaking strength and the traverse breaking strength reduce by 21.53% and 60.32% respectively, and the longitudinal breaking stretching ratio and the traverse breaking stretching ratio reduce by 63.07% and 64.17% respectively. 2) Under uniaxial tensioning, the longitudinal breaking strength and the traverse breaking strength reduce by 5.84% and 57.14% respectively, and the longitudinal breaking stretching ratio and the traverse breaking stretching ratio reduce by 68.06% and 68.47% respectively. 