The sub assembly production line of underbody is capable of 6 kinds of car modes in mix-lined production, and its cycle time up to 65JPH with high spot count. Multiple underbody of mix-lined production is available in different floor plans depending on floor space and production speeds. The high-efficiency and heavy-load slide mechanism and flexible underbody locating system can achieve this. Scheduled production multiple underbody systems are also available at reduced floor space and cost. Under the requirements of high automation rate and production line speed, we adopt professional logistic gathering and discharging equipment, high speed roller bed and reciprocating lever (SHUTTLE) to realize the transmission during stations and different production areas. Meanwhile, we adopt several design methods modular and standardized to shorten the transition time among stations, optimize logistic venues, and set aside enough time for welding to improve welding quality.