The solar cell with impurity photovoltaic effect can make use of the solar photons with energies less than the bandgap so that its conversion efficiency could be improved. To improve the conversion efficiency of the GaAs solar cells by using impurity photovoltaic effect, the GaAs solar cells doped with nickel for impurity photovoltaic effect were investigated by numerical method. The influence of nickel-doping on the short-circuit current density, open-circuit voltage and conversion efficiency was investigated. The effect of trapping structure on the cell performance was discussed. The results show that an increase of the conversion efficiency 3.32% can be achieved due to the impurity photovoltaic effect. The improvement of the solar cell performance attributes to the absorption of some sub-band photons, which results in the extension of the infrared response. Moreover, a good light trapping should be required to obtain better device performance for solar cells with impurity photovoltaic effect. It can be concluded that nickel doping in GaAs solar cells with impurity photovoltaic effect is a promising way for higher efficiency.