Five deleted mutants of HC-Pro gene of Chinese isolate of potato Y potyvirus (PVY-C) were obtained by PCR mutation, and their plant expression vectors were constructed. They were transformed into tobacco K326 (Nicotina tabacum cv. K326) mediated by Agrobacterium. PCR and Southern blot analysis revealed that PVY-C HC-Pro gene and its deleted mutants were integrated into tobacco genome, and Western blot analysis showed that they were all expressed in transgenic tobacco plants. Furthermore, infection test demonstrated that the central region of PVY-C HC-Pro can mediate synergism of PVY-C/cucumber mosaic cucumovirus (CMV) and PVY-C/potato X potexvirus (PVX), identifying that it is functional domain in synergism.