Aiming at the characteristics of multi-station, complex tasks, and extensive control requirements of motor assembly lines, a multi-PLC control system based on PROFINET technology is designed. Utilizing Siemens products, the PROFINET IO control system is configured, with the Siemens S7-1500 PLC serving as the IO controller for overall scheduling, logical operations, and data processing. Four Siemens S7-1200 PLCs function as intelligent IO devices, managing motion control, while the Siemens KTP900 touch screen facilitates real-time control and monitoring. The paper explores communication control between multiple PLCs and employs WinCC configuration software to design the monitoring interface, analyzing the communication control between PLCs and the touch screen. The program structure is designed based on modularization principles, wherein each workstation corresponds to a subroutine. Workstations operate relatively independently of one another but can be flexibly combined as needed. They are organically integrated through specific interfaces, which significantly enhances the flexibility and portability of the motor assembly line system.