Abstract: Abstract: With the development of information technology and people's awareness of food safety, traceability information technology has become an indispensable technology and tool for food and agricultural enterprises to handle quality and safety accidents, achieve product traceability, and solve the problem of defective products in time. Grain has a strategic position in China. The Chinese government and people have attached importance to the quality and safety of food. Wheat flour was one of the main grain products. However, the wheat flour processing was a complex technique, which was made up of many links, and had complicated batch mixing. Due to these characteristics, the traceability information of wheat flour quality and safety was crossed and it was difficult to trace the single individual. Most of the current tracing methods were not suitable for wheat flour traceability. Therefore, there was a pressing need to improve the precision of wheat flour tracing and solve its quality and safety problems by using raw materials and product batches as traceability units in wheat flour traceability. First of all, through case investigation, the processing flow of wheat flour was summarized, and the key nodes and traceability information affecting the quality and safety of wheat flour in the process were analyzed in this study. Then, the concept of batch list was introduced and the construction process was improved. The composition relationship and activity process of wheat flour and raw materials batch were analyzed. The relevant parameters in the production line such as flow volume and storage capacity were added to build and update the batch list based on the node processing time. Gozintograph method was used for data storage. The construction process and information tracing of BOL (bill of lots) were described in detail, which can achieve the accurate tracing of product information and key node activity information. On the basis of BOL's "parent-child" node, the location of wheat flour quality traceability points, hazard indicators, and structural relationships between nodes were clearly described using fishbone maps. The fishbone map was transformed into Petri net to construct the Petri net model of quality and safety relationship during wheat flour processing. The information that affected wheat flour quality and safety in wheat flour processing, such as laboratory results and environment conditions, was decomposed and quantified. The entire process of quality tracking hazard change was expressed by defining Petri Net's six-tuple. The dynamic characteristics of Petri net were used to estimate the pathway of hazard propagation, and the efficiency was improved. The batch list of wheat flour was constructed by using practical cases to prove the accuracy of Petri net and the feasibility of the tracing method. The results showed that BOL can analyze material batch information and activity information, and trace the information of wheat flour processing. By using the tracing model for wheat flour processing based on BOL and Petri, the number of recalled batches was reduced from 7 to 4 and the number of hazards searched was reduced from 6 to 5 compared to the traditional method. The Petri net model can quickly and effectively predict the hazard propagation pathway and improve the tracing accuracy of wheat flour and the efficiency of defects recalling. The results provide theoretical support for the traceability of grain and other small-sized products, as well as the information technology of traceability for related production enterprises.