In this paper, the concept of electrical potential influencing factor is proposed to describe the effect of electrical potential difference between the dust particle and background plasma on conductivity, based on which the conductivity model of dusty plasma is improved. The electrical potential influencing factor is directly proportional to the charge number, number density, radius of the dust particle, and the electron number density of the background plasma. Meanwhile, it is inversely proportional to the electron temperature of the background plasma. Taking rocket exhaust plume for example, the conductivities with and without considering potential difference are given both in the microwave and near infrared regions. In the given dusty plasma parameters condition, the influence of electrical potential difference on electrical conductivity reduces as the incident frequency increases. When the frequency increases to the near-infrared light region, the influence of electrical potential difference on the imaginary part of the conductivity can be ignored.