The invention provides a spectrum measuring method. The spectrum measuring method comprises the following steps of calibrating a spectrum measuring system, measuring the transmittance of samples to be measured, computing an extinction spectrum of the samples to be measured, measuring the samples to be measured after loading the samples to be measured in a reference sample pool or a sample pool, converting the samples to be measured in the reference sample pool or the sample pool into standard samples, calibrating the reflectivity of a second reflection lens, the reflectivity of a third reflection lens, the distance r between the samples to be measured and a photoelectric detecting and processing unit, and the transmittance of a attenuation slice, and computing and obtaining the scattered spectrum of positions near 90 degrees of the samples to be measured.