Foxtail millet and sourdough are used to make foxtail millet sourdough steamed bread to improve the flavor and taste. Compared with the conventional freeze-thaw treatment (CFT), the effect of magnetic field-assisted freeze-thaw treatment (MFT) on the storage quality of foxtail millet sourdough and steamed bread is explored. The results showed that compared with CFT, MFT shortened the phase transition time of dough; decreased the water loss rate, the water mobility, and the freezable water content; increased the fermentation volume; stabilized the rheological properties; and minimized the damage of freezing and thawing to the secondary structure and microstructure of the gluten. In addition, an analysis of the specific volume, texture, surface color, and texture structure showed that MFT was beneficial to slowing the deterioration of the steamed bread texture. Finally, MFT effectively inhibited the growth and recrystallization of ice crystals during freezing and thawing, improving the quality of millet dough and steamed bread.