In this paper, hydrophilic domain of DjHSP70 was predicted by using internet biosoftware. The DjHSP70 C-terminal contains numerous hydrophilic amino acids. Based on this hydrophilic domain of DjHSP70, the prokaryotic expression vector was constructed. PCR method was used to amplify 450 bp cDNA fragment encoding DjHSP70 C-terminal 150 amino acid polypeptides. After digested by Hind Ⅲ/XhoⅠ, this cDNA fragment was ligated to pET-28a expression vector. Recombinant plasmid was transformed into E.coli BL21 and a 21 ku fusion protein was expressed after the induction with IPTG, which was in agreement with the expected molecular weight. This fusion protein was purified using Ni²⁺-NTA agarose and detected by SDS-PAGE electrophoresis. Grayscale scanning showed that the purity of the purified protein was over 95%. The fusion protein was used as an antigen to immunize New Zealand rabbits to prepare the polyclonal antibody. The results showed that this anti-serum was not only very specific to DjHSP70, but also recognized mouse HSP70.This work has laid the foundation for further investigating stress responses in freshwater planarians.