When the body, main support and other large metal parts are damaged, welding or surfacing is generally used as the repair method. Measuring volume of repair is a key step before welding repair, because former provides relevant parameters for latter. Line structured light detection is a fast and convenient machine vision detection method, which is suitable for detection tasks in various complex environments and satisfies the requirements of volume of repair of engineering equipment detection. This paper designs a scheme based on line structured light. In this scheme, the parameters of welding repair are obtained by several steps, such as scanning, image processing, light strip center extraction and trend points extraction. Compared with other common methods, this scheme has the advantages of fast detection, easy operation, high cost-performance ratio and easy expansion. especially in combination with welding robots, it can greatly improve the level of automation and reduce the maintenance time.