The invention provides a protein used for broad spectrum detection of Bt (bacillus thuringiensis) Cry toxins as well as a coding gene and application thereof. The DNA (deoxyribonucleic acid) sequence and amino acid sequence of the protein are respectively shown in SEQ ID NO.1 and SEQ ID NO.2. The protein provided by the invention has better binding activity with five Bt Cry toxins (Cry1Ab, Cry1Ab, Cry1B, Cry1B and Cry1F) and can be used for broad spectrum detection of Bt toxins of wheat samples. The single-domain antibody protein used for broad spectrum detection of Bt Cry toxins, which is obtained without animal immunization, is short in preparation cycle, has a small amino acid sequence, is suitable for in vitro large-scale production and has important scientific and practical significance in developing rapid detection kits.