The invention discloses a vaccine for preventing decayed tooth and a preparation method thereof. Active ingredients of the vaccine for preventing a decayed tooth are proteins shown as 1) or 2) or 3): wherein 1) a protein is composed of amino acid sequences shown as a sequence 2 in a sequence table1; 2) a protein is derived by 1), relative to the prevention of the decayed tooth and formed by the fact that one or more amino acids is/are substituted and/or lost and/or added on amino acid sequences of the sequence 2 in the sequence table; and 3) a protein is composed of amino acid sequences shown as 9th position to 419th position of the sequence 2 in the sequence table. The vaccine has the advantages that the vaccine has a solubility expression and is easy to purify, the purity is high, the preparation method is simple and convenient and the like, and besides, the vaccine has remarkable economic benefits and can be used as a candidate vaccine for preventing the decayed tooth caused by streptococcal infections.