Using monocrystalline silicon, multicrystalline silicon and simulated amorphous silicon solar cells as research objects, we study the influences of bias spectral characteristics such as irradiance and spectral distribution on the spectral response (SR) of solar cells. The SR of solar cells is related to the bias light. The SR at long wavelength region increases and the short-circuit current of solar cell increases linearly with the increase of irradiance of bias light. The spectral distribution of bias light also has influence on the SR of solar cell. Large spectral mismatch degree induces large difference in SR measurement. Therefore, the irradiance and spectral distribution of bias light should be as close as possible to the IEC standard in order to improve the accuracy of SR measurement of solar cells.