Abstract: Perforation occurred in a water injection flexible composite pipe. The causes of perforation were analyzed by macroscopic observation, density, hardness, Vicat softening temperature, crosslinking degree test, infrared spectrum analysis, thermogravimetric and tensile strength test. The results show that the water injection pipe was a type I flexible composite pipe, but the wall thickness didn’t meet the standard requirements. The lining material was ordinary polyethylene, local resin was missing, and there was cracking and perforation at the most serious place. The color of the contaminated fiber became darker and brittle fracture occured. There was a perforation at the same position of the outer protective layer and the inner lining. The reason for the perforation of the composite pipe was the lack of resin in the inner liner, and the high salinity medium penetrated into the reinforced fiber layer, resulting in a significant reduction in its mechanical properties.