This paper presents a systematic study of the ground-state binding energies of a hydrogenic impurity in quantura dots subjected to external electric and magnetic fields. The quantum dot is modeled by superposing a lateral parabolic potential, a Gaussian potential and the energies are calculated via the finite-difference method within the effectivemass approximation. The variation of the binding energy with the lateral confinement, external field, position of the impurity, and quantum-size is studied in detail. All these factors lead to complicated binding energies of the donor, and the following results are found： （1） the binding energies of the donor increase with the increasing magnetic strength and lateral confinement, and reduce with the increasing electric strength and the dot size; （2） there is a maximum value of the binding energies as the impurity placed in different positions along the z direction; （3） the electric field destroys the symmetric behaviour of the donor binding energies as the position of the impurity.
