The invention provides an avian adenovirus fiber protein subunit vaccine. A new-type antigen fiber protein of an avian adenovirus is used, after a sequence is optimized, the fiber protein acquires soluble expression in escherichia coli, and an expression product is used for preparing the subunit vaccine, wherein an amino acid sequence of the avian adenovirus fiber antigen protein is SEQ ID NO: 4,and a nucleotide sequence of an encoding gene thereof is SEQ ID NO: 3. The subunit vaccine prepared by the avian adenovirus fiber protein has the characteristics of high antigen stability, high purity, strong specificity, no generation of other uncorrelated antibodies, and convenient and accurate detection method. A firm foundation is established for industrially producing the avian adenovirus subunit vaccine and diagnostic reagent.