The invention discloses a peanut cysteine protease encoding gene AhRD21A, the construction of an overexpression vector of the peanut cysteine protease encoding gene AhRD21A and the application of the peanut cysteine protease encoding gene AhRD21A in tobacco bacterial wilt resistance genetic engineering. The gene contains a nucleotide sequence as shown in SEQ ID No. 1. The CaMV 35S promoter-driven overexpression vector agrobacterium-mediated transformation bacterial wilt susceptible variety Honghua Dajinyuan is constructed through a Gateway system, molecular detection and ralstonia solanacearum inoculation recognition are carried out on transgenic plants, and overexpression of the CaMV 35S promoter-driven overexpression vector agrobacterium-mediated transformation bacterial wilt susceptible variety Honghua Dajinyua in tobaccos can significantly improve bacterial wilt resistance of transgenic tobaccos. The result shows that the AhRD21A may participate in the resistance reaction of the plant to the bacterial wilt, which has an important gene resource for the bacterial wilt resistance genetic engineering breeding application of the plant.