A filter lens, an LED lamp with the filter lens, and an illumination system, the illumination system comprises an LED lamp with a filter lens, and an illuminated surface. The LED lamp with a filter lens comprises a light-emitting module, a collimating lens, and a filter lens, the filter lens comprises a light incident surface, and a light-emitting surface disposed on an opposite side of the light incident surface. The light incident surface comprises a plurality of irregular slot arranged end to end. Since the illumination system uses the LED lamp with a filter lens, and the filter lens of the LED lamp with the filter lens comprises the above-mentioned irregular slot, to adjust the positional relationship between the LED lamp with a filter lens and the illuminated surface. relative to the side of the illuminated surface that is closer to the LED lamp, the light directed to one side of the illuminated surface farther from the LED lamp can compensate for more attenuation due to reaching a distance from the LED lamp, it is possible to have substantially the same illuminance in which is near to or far from the LED lamp.