The formation of the underground mass of winter wheat, on the one hand, largely determines the survival of plants and, ultimately, the yield of the crop. And on the other hand, this process largely depends on the properties of the soil, and, above all, physical, as well as on the overall level of fertility. Monitoring the process of changing the root mass of plants during their development makes it possible to timely adjust this parameter using agrotechnical techniques. However, the control of this parameter is quite complicated, so the relevance of research aimed at optimizing the method of accounting for root mass is very relevant. We have proposed a method for determining the underground mass of winter wheat. The technical essence of the invention includes photographing the object, transferring the image to a computer, and then cropping the part under study. Further, through the processing of the resulting image using a histogram, an analysis of the output shades and distinctive features is carried out. The task of the method is based on obtaining new correlations between the mass and the spectral index of the image. The main component of the analysis is the percentile obtained by evaluating the histogram, namely, only the black area of the image and its shades. The calculation of the mass of the root system of wheat is carried out according to the formula: Mks=D×К, Mks is the mass of the root system t∙ha-1; D is the percentile of the histogram, %; and K is a constant coefficient (the ratio between the mass of the root system and the value of the percentile of the histogram). As a result of scientific research, a close correlation relationship (r = 0.98) was obtained between the mass of the root system (Mks) and the percentile of the histogram (D). This method of the invention makes it possible not only to simplify the determination of the mass of the root system of winter wheat, but also makes it possible to repeat measurements in digital format.