The invention discloses a chitinase for deactivating a varroa destructor, a serratia marcescens and application thereof. In the invention, the serratia marcescens for deactivating the varroa destructor is separated from intestines of Chinese worker bees and is stored in a Chinese typical culture storage center with a storage number of CCTCC M 209097; a gene base sequence is cloned from the serratia marcescens, and a procaryon expression carrier pET-32a(+) is applied to express the gene in a colon bacillus. Purification, renaturation and bioassay are carried out on a protein coded by the gene,a result shows that the protein coded by the gene has stronger toxicity to the varroa destructor, and sequencing analysis shows that the protein is a new sequence of chitinase gene ChiA types. The invention can be used for preventing the mite damage of bees.