Abstract: When pipelines are in operation, pipeline defects may result in pipeline failures, such as deformation, leakage and even crack. Composite materials based reinforcement and repair technology is currently the principal method for the reinforcement and repair of oil and gas pipelines thanks to its safe, convenient and fast attributes. In order to ensure the best repair effect for the defects and improve the repair strength and performance of composite materials, the factors influencing the mechanical properties of composite materials were tested in terms of numerical simulation and samples preparation test in Laboratory, e.g., wetting degree, gel content, moisture and sandy wind, combined with the effect of repairing engineering for pipeline body defects over the years. It is concluded that wetting degree and gel content are the most important influential factors, and the quantity of reinforcement layers has enormous effect on the strength of repaired pipelines. Damage resisting capacity of pipelines increases with the increasing of the quantity of reinforcement layers which is made of composite fiber materials.