The invention provides a spectrum analyzing method and device for soil oxidation-reduction potential above an oil and gas reservoir. The spectrum analyzing method comprises the steps that soil samples at the set depth of the oil and gas reservoir and the peripheral superficial part of the oil and gas reservoir are collected; the oxidation-reduction potential of the soil samples is measured; the reflectivity spectrums of the soil samples are measured, spectrum jumps, at the set wavelength positions, of the soil samples are eliminated, the reflectivity spectrums are processed again, and the three derivative spectrum indexes of a reflectivity first-order derivative, a reflectivity second-order derivative and the reflectivity absorption depth are generated; related coefficients between the oxidation-reduction potential and the reflectivity spectrums, the reflectivity first-order derivative, the reflectivity second-order derivative and the reflectivity absorption depth are calculated; the optimal modeling spectrum index and the modeling wavelength are determined according to the related coefficients; a regression model between the oxidation-reduction potential and the optimal spectrum index is established through the least square method.