The present invention provides an optimized immobilization antigen cDNA sequence of cryptocaryon irritans, which has been processed codon replacement and caused the cDNA to express in prokaryotic and eukaryotic cell and translate a protein has similar immunogenicity as the immobilization antigen purified from the theront of Cryptocaryon irritans. The present invention further provides a DNA vaccine produced using the cDNA to prevent fish form cryptocaryon irritans infection.