BackgroundRaw starch-degrading α-amylase (RSDA) can hydrolyze raw starch at moderate temperatures, thus contributing to savings in starch processing costs. However, the low production level of RSDA limits its industrial application. Therefore, improving the extracellular expression of RSDA inBacillus subtilis, a commonly used industrial expression host, has great value.ResultsIn this study, the extracellular production level ofPontibacillussp. ZY raw starch-degrading α-amylase (AmyZ1) inB. subtiliswas enhanced by expression regulatory element modification and fermentation optimization. As an important regulatory element of gene expression, the promoter, signal peptide, and ribosome binding site (RBS) sequences upstream of theamyZ1gene were sequentially optimized. Initially, based on five single promoters, the dual-promoter Pveg-PylBwas constructed by tandem promoter engineering. Afterward, the optimal signal peptide SPNucBwas obtained by screening 173B. subtilissignal peptides. Then, the RBS sequence was optimized using the RBS Calculator to obtain the optimal RBS1. The resulting recombinant strain WBZ-VY-B-R1 showed an extracellular AmyZ1 activity of 4824.2 and 41251.3 U/mL during shake-flask cultivation and 3-L fermenter fermentation, which were 2.6- and 2.5-fold greater than those of the original strain WBZ-Y, respectively. Finally, the extracellular AmyZ1 activity of WBZ-VY-B-R1 was increased to 5733.5 U/mL in shake flask by optimizing the type and concentration of carbon source, nitrogen source, and metal ions in the fermentation medium. On this basis, its extracellular AmyZ1 activity was increased to 49082.1 U/mL in 3-L fermenter by optimizing the basic medium components as well as the ratio of carbon and nitrogen sources in the feed solution. This is the highest production level reported to date for recombinant RSDA production.ConclusionsThis study represents a report on the extracellular production of AmyZ1 usingB. subtilisas a host strain, and achieved the current highest expression level. The results of this study will lay a foundation for the industrial application of RSDA. In addition, the strategies employed here also provide a promising way for improving other protein production inB. subtilis.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12934-023-02116-z.