A fish-derived peptidoglycan recognition protein mutant and an application thereof are provided. An amino acid sequence of the mutant is shown in SEQ ID NO. 1, a nucleotide sequence of the mutant is shown in SEQ ID NO. 2. The present disclosure provides the preparation method for the mutant with a broad-spectrum antibacterial activity and robust inhibitory effects on both Gram-positive and Gram-negative bacteria. Compared with the wild-type LcPGRP5 protein, the mutant protein demonstrates a stronger ability to inhibit the activity against Staphylococcus aureus and enhance the phagocytic ability of fish macrophages.