Abstract: Cysteine proteaseinhibitor(CPI) is closely related to plant disease and insect resistance. In order to clarify the function of tobacco CPI (NtCPI) and its relationship with tobacco resistance to aphids, the expression of NtCPI1 in different tobacco varieties were analyzed by qRT-PCR before and after raphid infestation. The results of qRT-PCR showed that the expression of NtCPI1 gene in resistant tobacco varieties was significantly increased after infestation of aphids. The expression of NtCPI1 in tobacco cultivar 664-01 after three hours of aphid infestation was 10.8 times higher than that in plants of control inoculation. The NtCPI1 expression in cultivar Blue River after six hours of aphid infestation was 6.28 times higher than that in plants of control inoculation. However, the expression of NtCPI1 in aphid susceptible cultivars, such as Luositou 2474, Yunyan 97 and Zhongyan 100, decreased significantly after insect infestation. NtCPI1 can be used as a highly effective anti-insect gene and has application potential.