The invention belongs to the field of biotechnology. In order to prepare a natural brown alga extracting solution with the high content of alginic acid under mild conditions in an efficient way, and retain more active substances of brown algae, a method for preparing the brown alga extracting solution by using a microbial enzyme-linked fermentation way is used according to the technical scheme andis characterized in that dry-basis brown alga powder and water are mixed to form a fermentation substrate, then a pre-fermentation liquid is added into the fermentation substrate, and according to the way of replenishing dry-basis brown alga powder in stages, the brown alga extracting solution is obtained by fermentation in a fermentation tank. According to the method, by an enzyme-linked fermentation technology, the brown alga extracting solution with a high concentration of alginic acid can be efficiently obtained, the content can reach 5-7%, more natural active substances are retained, andenergy consumption and active-ingredient loss which are caused by subsequent concentration are avoided.