Abstract: Aiming at the problems of unintuitive monitoring of abnormal cylinder actuation, easy repeated recording of alarm information, and insufficient timer resources of traditional PLC in automatic production lines, a cylinder fault alarm program based on data blocks is designed. Soft timers are constructed using DB data blocks to solve the problem of limited timer quantity in old PLC systems such as S7-300. By optimizing the program scanning sequence and alarm flag mapping mechanism, the flickering and repeated recording of alarm information on the HMI interface are avoided. Single-action buttons, output status and abnormal indicators are integrated in the touch screen to realize rapid fault location. Engineering applications show that this scheme has a clear structure, strong universality and high portability, which can effectively improve the efficiency of equipment commissioning and troubleshooting, and provide a reference for the design of alarm systems for similar automatic equipment.