The invention discloses a negative ion photocatalyst lamp comprising a lamp cap, a lamp tube, a ballast and a negative ion generator. The ballast is connected between the lamp cap and the lamp tube, fluorescent powder coated in the lamp tube, and the ballast and the negative ion generator share one set of a filtering circuit and a rectifying circuit. The fluorescent powder comprises rare earth trichromatic fluorescent powder and ultraviolet fluorescent powder. Because the photocatalyst lamp can be used as an illuminating lamp, the invention can also effectively trigger the redox of the photocatalyst lamp, additionally simplifies a circuit of the prior negative ion energy-saving lamp, and prevents the occurrence of harmful harmonic wave and radiation pollution due to a negative ion generating device.