7.69%减小到3.76%。The principles and methods were introduced for measuring soil organic matter content with the aid of spectrum data diffusely reflected by the soil. The arrangement scheme，light system, hardware and software were carefully designed. In order to further decrease the measurement errors, on the basis of previous research, three other signals from different wavelengths of light were used——including the variation of “deviation of arch” for soil spectra at 600 nm. Different processing procedures of soil samples were used for analyzing the influence on precision of organic matter content. The results showed that the measuring precision between the measurements obtained by this system and by standard methods were remarkably improved and measuring errors were reduced from 7.69% to 3.76% obviously by including the variation of “deviation of arch” within the permissible range for practical use. 