The present disclosure provides an antimicrobial alginate fiber, a method for manufacturing an antimicrobial alginate fiber dressing thereof, and an application thereof. When the cationic polymer polyhexamethylene guanide salt is mixed with the anionic polymer alginate, the antimicrobial activity of the guanide salt is quickly passivated. The present disclosure achieves a lower content of polyhexamethylene guanide salt in an alginate dressing with good long-term antimicrobial activities. The polyhexamethylene guanide salt has a low dissolution rate, and significantly reduces a potential risk of carcinogenicity, mutagenicity and reproductive toxicity.