Abstract: A gene PpHSP21 with black spot disease resistance is isolated from Pyrus pyrifolia. A nucleotide sequence of the gene PpHSP21 is shown in SEQ ID NO. 1. An amino acid sequence of an encoded protein of the PpHSP21 gene is shown in SEQ ID NO. 2. By constructing the plant overexpression vector and silencing vector of the gene PpHSP21, the gene PpHSP21 is introduced into the plant by the Agrobacterium-mediated genetic transformation method, so that the gene PpHSP21 is able to be overexpressed in the plants, thereby significantly improving black spot disease resistance in plants. The discovery and identification of the gene PpHSP21 provide new genetic resources for stress resistance molecular design and breeding in plants, and to provide new genetic resources for the implementation of green agriculture. The development and utilization of the genetic resources is conducive to reducing agricultural production costs and achieving environmental friendliness.