The invention discloses a strain of Streptococcus agalactiae phage, and applications thereof. According to the present invention, the phase capable of efficiently lysing Tilapia derived Streptococcusagalactiae is firstly separated and purified, and the biological characteristics of the phase are studied so as to provide the theoretical basis for the further development and utilization of the phage; and the phage therapy is firstly used for preventing and treating e to prevent and treat Tilapia Streptococcus agalactiae diseases so as to break the abuse of antibiotics and chemicals in the previous treatment mode, such that the drug resistance of bacteria can be reduced, the efficient and safe treatment has great development potential, and the significant social and economic benefits can beachieved.