The invention relates to an image sensor absolute spectral response degree testing device and an image sensor absolute spectral response degree testing method and belongs to the space optics technical field. The objective of the invention is to solve the problem of large deviation in image sensor absolute spectral response degree testing. An integral ball collector is installed at the light outlet of a monochrometer; the normal of the light inlet of the integral ball collector is vertical to the normal of the light outlet of the integral ball collector; monochromatic light emitted by the monochrometer enters the integral ball collector through the light inlet of the integral ball collector; and a uniform emergent light spot is formed at the light outlet of the integral ball collector. A standard trap radiometer is adopted to test radiation energy at the light outlet of the integral ball collector; and based on the area of the light outlet of the integral ball collector, radiant illuminance at the light outlet of the integral ball collector is calculated. When an image sensor is tested, the light sensing pixel region of the image sensor is attached to the light outlet of the integral ball collector, so that an corresponding image can be obtained; based on the area of pixels, radiation energy obtained by the image sensor is calculated; and based on the obtained radiation energy and output signals of the image sensor, parameters such as the absolute spectral response degree and quantum efficiency of the image sensor can be calculated conveniently.