Multi mode DCS is an industrial automation control system composed of multiple distributed control units, each of which can achieve different control modes. The control logic involved in this system is relatively complex, requiring consideration of issues such as switching, parallelism, and priority of multiple different control modes, which increases the difficulty of the control process. To this end, a multi-mode DCS automatic control module is designed using a small PLC. Using small PLC components as module controllers, adjust the internal structure of sensors, processors, DCS frequency converters, communication networks, etc., and complete the hardware design of multi-mode DCS control modules through circuit connections. Collect real-time operating data of industrial automation production lines, use feature extraction and matching methods to identify the current operating mode of the production line, use a small PLC to generate automation production line control commands, and transmit them to various production line work equipment in a decentralized manner. Finally, multi-mode DCS control functions will be implemented in terms of working mode, position, speed, and other aspects. The test results show that the position and speed control errors of the design module have been reduced by 35mm and 83.75r/min, respectively, which can effectively improve the qualification rate of the output products of the production line.