Based on the framework of effective-mass approximation and variational approach, the influence of built-in electric field and impurity on the binding energy of a cylindrical wurtzite GaN/Alx Ga1-x N quantum dot(QD) with two electrons is discussed. The numerical results show that while the charge of impurity is negative, the impurity state is instable. When there is a donor impurity with positive charge e in the center of QD, the binding energy of impurity to electron firstly increases slowly, reaches a maximum value, then decreases with increasing the height and radius of QD. With increasing Al content, the binding energy increases monotonically. The binding energy of impurity to electron firstly increases, and then decreases with moving the impurity position from the bottom of QD to the top, there is a maximum. In comparison with the single-electron impurity states, the influence of the built-in electric field on the binding energy of two-electron quantum dot system is more obvious. While the QD height L<6 nm in the WZ GaN/Al0.15 Ga0.85 N QD with the radius R=5 nm, the binding energy of two-electron quantum dot system with impurity is larger than that of the single-electron impurity states. While the QD height L>6 nm, the binding energy of two-electron quantum dot system with impurity is smaller than that of the single-electron impurity states.