Objective:To prepare anti-human IgE nanobody by phage display technology,and to establish a method for hyper-sensitivity detection of cat dander specific IgE antibody.Methods:Allergen bio-information of cat was searched in WHO/IUIS Allergen Database.After synthesizing sequence,recombinant cat dander allergenic protein Fel d 1 was expressed and purified in prokaryotic ex-pression system.Human IgE was used to immunize Bactrian camel and RNA were extracted from lymphocyte to construct phage dis-play library.Library capacity,diversity and insertion rate were analyzed,anti-human IgE nanobody were obtained by screening and identification.A magnetic particle chemical method for cat dander specific IgE antibody detection was established using recombinant allergen-coupled magnetic particles and acridine ester-labeled nanobodies.Results:Capacity of phage display library was 1.88×108 cfu/ml,insertion rate was 93.6%,and purity of nanobody was>95%.Linear range of the method based on nanobody was 0.1～100 U/ml,who was consistent with ImmunoCAP detection system by clinical data.Conclusion:Nanobody-based cat dander specific IgE antibody hypersensitivity assay is successfully prepared,providing a technical basis for auxiliary diagnosis of cat allergic diseases.