A variational method is adopted to investigate the properties of shallow impurity states near the interface in afree strained wurtzite GaN/AlxzGal1-xN heterojunction under hydrostatic pressure and exteal electric field by using asimplified coherent potential approximation.Considering the biaxial strain due to lattice mismatch or epitaxial growthand the uniaxial strains effects,we investigated the Stark energy shift led by an exteal electric field for impurity statesas functions of pressure as well as the impurity position,Al component and areal electron density.The numerical resultshows that the binding energy near linearly increases with pressure from O to 10 GPa.It is also found that the bindingenergy as a function of the electric field perpendicular to the interface shows an un-linear red shift or a blue shift fordifferent impurity positions.The effect of increasing x on blue shift is more significant than that on the red shift for theimpurity in the channel near the interface.The pressure influence on the Stark shift is more obvious with increase ofelectric field and the distance between an impurity and the interface.The increase of pressure decreases the blue shiftbut increases the red shift.