The invention discloses a double-signal lung cancer exhalation gas detecting system which comprises a fluorescence detection device, a visible light detection device, a gas reaction device and a spectrograph, wherein the fluorescence detection device comprises a fiber-optic probe, an excitation light source supporting table, a motor I, an excitation light source transfer table, an optical filter installation plate and a rotation shaft I; the visible light detection device comprises a light-emitting diode (LED) light source plate and a camera; the gas reaction device comprises a motor II, a gas reaction chamber, a reaction table, a rotation shaft II, a porphyrin sensor thin piece, an air pump and a driving mechanism driving the motor II to horizontally move; the gas reaction chamber is located between the fluorescence detection device and the visible light detection device; and the gas reaction chamber is higher than the LED light source plate and the excitation light source transfer table and lower than the camera and the optical filter installation plate. With the adoption of the double-signal lung cancer exhalation gas detecting system, two kinds of signals including fluorescence spectra and visible light colors are adopted to measure simultaneously, detection is carried out through cross response, and the detection is rapid and high in sensitivity, so that detection accuracy is greatly improved, the price is low, and the operation is simple.