According to the relevant testing standards of fiber mechanical properties，the testing method of tensile properties of high model PBO bundle fiber was studied systematically.The results show that the clamping fixture and ceramic material fixture body are suitable for the tensile test of PBO dry yarn.The twist coefficient has a great influence on the tensile properties of PBO，and the optimum value is 8.It is found that twisting will affect the orientation degree of fiber.The increase of the stretching speed will increase the fracture strength of the fiber.The pre-tension has little influence on the tensile properties of the PBO fiber within the testing range.The longer the clamping length is，the closer tensile deformation measured by the crossbeam is to the real value.