The invention discloses a protein. The provided protein is the following protein (1) or (2): the protein (1) is formed by an amino acid sequence shown by a sequence 2 in a sequence table; and the protein (2) is formed by the amino acid sequence of the sequence 2 in the sequence table through the substitution and/or deletion and/or addition of one or several amino acid residues, can be combined with IgE molecules and is derived from the protein (1). The protein has higher affinity with the IgE; Fc epsilonR I alpha and IgG2 are both derived from humanized protein, and the protein has no antigenicity, does not need humanized reconstruction, has a longer half life, and has the molecular weight of 170kDa which is larger than the molecular weight of sFcepsilonR I alpha. The protein has potential value on treating anaphylactic diseases including asthma, allergic rhinitis, atopic dermatitis, food allergy and the like.