Within the framework of effective-mass approximation, the ground-state donor binding energy of a hydrogenic impurity in cylindrical wurtzite (WZ) symmetric ZnO/MgZnO strained coupled quantum dots (QDs) is calculated by means of a variational method, considering the strong built-in electric field induced by the spontaneous and piezoelectric polarizations. Numerical results show that the strong built-in electric field induces an asymmetric distribution of the donor binding energy with respect to the center of the coupled QDs. When the impurity is located at the center of the dot which is opposite to the growth direction, the donor binding energy has a maximum value with increasing dot height; and it is also insensitive to the middle barrier width if the middle barrier width is large. Moreover, numerical results also indicate that the donor binding energy of impurity located at the right boundary of the dot which is opposite to the growth direction is insensitive to the Mg composition if the Mg composition is large. (C) 2010 Elsevier B.V. All rights reserved.