The invention relates to a repair welding clamp for lower body of light weight vehicles. The invention belongs to the automobile manufacturing industry field. The repair welding clamp for lower body of light weight vehicles is provided based on disadvantages that conventional welding device adopts mainly manual operation or is low in automation, so that the welding efficiency is low or the welding quality is low and cost is high. The repair welding clamp includes mainly an adjustable bracing frame, an I-shaped bracing body, an operation platform, positioning devices, locking devices, an electrical system or the like. The operation platform has six sets of positioning devices, eight sets of positioning clamping devices and can be latched dynamically and randomly by latching devices. The positioning locking devices are arranged in a symmetric manner, bear balanced force and have a linkage function. The positioning and locking devices can be adjusted dynamically according to different types of light weight cars and different positioning positions different lengths of vehicles and changes of different structures of vehicles. The repair welding clamp is used for four vehicle types such as single-row cars, double-row cars, vans and half-row cars. The repair welding clamp not only has a simple structure, is economical and practical, reduces labor intensity of operation and improves production efficiency, but also has the characteristic of being suitable for lower bodies of vehicles of various kinds. The repair welding clamp serves as one machine used for various vehicles and helps to realize flexible production.