Porphyra yezoensis is a widely cultivated red alga. P. yezoensis is the most economically valuable species among artificially cultivated seaweeds in China. However, microbial exceedance in roasted P. yezoensis products has frequently occurred, affecting the development of the P. yezoensis industry. Dry P. yezoensis is the raw material used for the original roasted (sushi laver) as well as roasted and flavored (laver) products. The microbial load in dry P. yezoensis is the main factor causing the aerobic plate count in roasted P. yezoensis products to exceed the standard. The use of substandard raw materials has resulted in huge economic losses for companies processing roasted P. yezoensis. Therefore, the changes in the aerobic plate count, bacterial community structure, and dominant bacteria during the dry P. yezoensis processing must be analyzed for developing effective microbial control methods. Fresh P. yezoensis is subjected after harvesting to a series of processes to obtain the final dried products: impurity removal, cleaning, dehydration, cutting, blending, cake-pressing and dehydration, first drying, and secondary drying. The raw algae, cleaning, blending, initial drying, and secondary drying are the five critical aspects among these steps that affect the aerobic plate count. Dried P. yezoensis samples were selected from three representative enterprises in different maritime regions in Jiangsu Province, China, to analyze the changes in the aerobic plate count and bacterial community structure during processing, and the dominant bacteria were screened. The plate count method was used to analyze the variations in the aerobic plate count at five steps processing critical. The total bacterial community in the samples was examined using 16S amplicon high-throughput sequencing. The structural characteristics of the total and culturable bacterial communities in the samples during the drying step were compared. The dominant bacteria were isolated and identified, and their tolerance to the processing steps were analyzed. The number of bacteria decreased after washing. The aerobic plate count of the samples inconsistently changed after drying, and the drying process did not produce substantial sterilization effects. The aerobic plate counts of the samples from two enterprises substantially increased after the first drying process for two reasons. First, the samples were contaminated if the sponge was not replaced as needed during cake-pressing dehydration. Second, the low-temperature and high-humidity environment during the initial drying was conducive to bacterial proliferation. The number of microorganisms in the samples did not markedly decrease after the second drying process, indicating that the high-temperature process did not sterilize the samples, and that the microorganisms were not effectively controlled or reduced. The raw seaweed harbored a diverse bacterial community, with relatively high abundances of Olleya, Maribacter, Octadecabacter, and Sulfitobacter. The bacterial flora structures widely differed with the algal harvesting area. The diversity of the total bacterial community decreased after drying, and Cyanobacteria became the dominant bacteria. The dominant culturable bacteria were Macrococcus, Deinococcus, Bacillus, Acinetobacter, and Chryseobacterium. The isolated dominant bacterium, Macrococcus, was poorly tolerant to high temperature but strongly resistant to drought. This study revealed the critical processing stages that increase the bacterial counts in dried P. yezoensis and the changes that occur in bacterial communities during processing. The tolerance of the dominant bacteria to drought and heat were preliminarily determined. These results provide the basis for controlling the microbial content in P. yezoensis during processing, laying a theoretical foundation for further the research and development of techniques for controlling bacteria in dried P. yezoensis.