The invention relates to a Bacillus saccharophila used for degrading alginic acid, and an application method thereof. The application method comprises the following steps: 1, milling dried alga to form powder, adding water to the alga powder according to a certain ratio, filling a fermentation tank with the obtained solution, and sterilizing the solution at a certain temperature for a period of time; 2, preparing a seed liquid: screening a fermentation strain YIC~ALG3 capable of degrading alginic acid, inoculating the fermentation strain YIC~ALG3 to a 2216E liquid medium, and culturing the fermentation strain YIC~ALG3 overnight; and 3, adding the obtained seed liquid to the fermentation tank according to a certain mass ratio, fermenting the seed liquid under certain conditions, and processing a brown alga raw material through using microbial fermentation to prepare an alga liquid. The fermentation process is stable and controllable, the fermentation period is short, and the alga liquid has substantial efficacy, and is suitable for large-scale production.