In this paper，we have calculated the impurity electronic states and the binding energy with the variation of the quantum dot radius and Al content in GaN/AlxGa1-xN spherical quantum dot (QD) using the plane wave method. The modification of the energy states is discussed when the difference in effective electron mass in GaN and AlxGa1-xN is taken into account. The results show that the difference in effective mass can not be neglected when Al content is large. In addition，with the consideration of the difference in effective mass，we investigate the binding energy as function of quantum dot radius, impurity position and external electric field. The results are meaningful and can be widely applied in the design of optoelectronic devices.