In 2017, the low pathogenic avian influenza H7N9 virus in China had mutated into high pathogenicity to domestic poultry, and led to a large number of poultry death and human cases. To evaluate the effect of virus mutation on the transmission of avian influenza H7N9 virus, this paper takes Guangdong province for the research area, takes domestic poultry, virus in the domestic poultry survival environment and human beings for the research objects, and establishes a non-autonomous dynamical model. By fitting model with the newly confirmed human cases in Guangdong province, the model we established is confirmed and applied to explain the dynamics of historical human cases. By carrying on parameter estimation, it is deduced that at least 5279376 human beings in Guangdong province had been infected with avian influenza H7N9 virus from March 2013 to September 2017, but most of them were not confirmed, since they had no obvious symptoms or had been cured as common influenza. And comparing with the low pathogenic avian influenza H7N9 virus (H7N9 LPAIV), the transmission rate of the highly pathogenic avian influenza H7N9 virus (H7N9 HPAIV) to human is almost unchanged, but to domestic poultry is about 3.87 times higher. Also, we calculate the basic reproduction number ?? = 1.3042, which indicates that the virus will persist in Guangdong province with time. Besides, we also perform some sensitivity analysis of the newly confirmed human cases and ?? in terms of model parameters and conclude that reducing the birth population of domestic poultry, speeding up the circulation of domestic poultry in the market and raising the rate of disease-related death of domestic poultry are benefit to control the transmission of the avian influenza H7N9 virus.