Abstract: In the automotive industry, the optimization of the process of manufacturing identical products in large quantities is the key to improving production efficiency. Robot automated production line is ideal for modern manufacturing. The existing research mainly focuses on the finite subproblem of the production line. This paper aims at the welding task assignment and welding sequence planning of multi-station and multi-robot production line in the actual automobile manufacturing industry. As well as many constraints of workpiece and production line composition are considered. The mathematical model of multi-station multi-robot welding task assignment and path planning (MSMR-WTAPP) is established. The optimization objectives are to minimize the first workpiece processing time, the subsequent workpiece processing time and the robot motion path length synchronously. An improved SPEA2 algorithm (SPEA2+IPD) based on Individual population density (IPD) is proposed. Aiming at the coupling problem of welding task assignment and welding sequence planning, a dual layer coding scheme is designed, and the decoding process of robot operation is addressed. Finally, the effectiveness and superiority of SPEA2+IPD algorithm in optimizing the production takt, efficiency and welding path of the production line are verified by simulation experiments. Compared with the actual production takt of the factory, the optimized production time of the first workpiece is shortened by 20.7%, and the production time of each subsequent workpiece is reduced by 15.2%, indicating that the proposed model and algorithm have practical significance for optimizing the production of the factory.