The utility model belongs to the technical field of railway traffic equipment overhauls and specifically relates to a multithreading assembly line for motor train unit overhauling. It includes: the main frame, go up plummer, upper assembly line, down plummer, lower floor's assembly line, head end assembly line lifting machine, terminal assembly line lowerator, move the machine of carrying, examine and repair a station, lower floor's assembly line lies in the below of upper assembly line, the conveying opposite direction of its direction of transfer and upper assembly line, moving the machine of carrying and installing on the main frame, its lift platform passes the plummer, the current -carrying waterline is moved to last the installing of lift platform. Adopting the design of two layers flow waterline, forming a loop configuration through head end assembly line lifting machine and terminal assembly line lowerator, the charging basket can loopback voluntarily, has effectively saved manpower and empty charging basket parking space, has improved efficiency, and the stopper can prevent that the empty charging basket process of loopbacking of bottom from colliding each other, can cushion the feeding and prevent that the station from stopping up, can be effectively passes on to the maintenance station labour saving and time saving with upper assembly line material through moving the machine of carrying.