Deep-level defects are the main cause of persistent photoconductivity (PPC) effect in wurtzite gallium arsenide nanowires (WZ GaAs NWs). The photoconductivity attenuation curve of WZ GaAs NWs are analyzed using the Gauss distribution based defect composite dynamics equation, and an average carrier capture barrier of 60.2 meV is obtained. By analyzing the transient behavior of photoconductivity under illumination, a defect photoionization model is proposed to extract the characteristics of specific defect energy levels. Through fitting the photoionization spectrum of WZ GaAs NWs, a photoionization energy of 0.69 eV is obtained. The large energy difference between the photoionization energy and the thermal capture energy implies that there is a strong coupling between the defect and the lattice for WZ GaAs NWs, which is similar to the behavior of EL2 center in zinc-blende GaAs.