Crab is one of the common allergic foods, the allergens of crabs are the source of crab sensitivity. Currently, the researches on the nature of allergens and the method of purification of allergens has attracted more and more attention, the major crab allergens are tropomyosin, arginine kinase and hemocyanin. The use of food processing technology to reduce allergenicity of crab is increasing, and many method including heating treatment, irradiation treatment, enzymatic treatment and high-pressure treatment have been developed to reduce the allergenicity of crabs. In this paper, the classification of allergen, preparation of allergenic proteins, cross-allergenicity between crabs and other crustaceans and method of reducing allergenicity were summarized, so as to provide theoretical basis for the diagnosis and prevention of the crab allergy, and offer a reference for the development of crabs with low allergenicity.