Processes of compaction of granular materials were described using selected models. The analysis of their accuracy on the example of wheat was the basis for the discussion on their applicability to the processing of plant-origin materials. Parameters of the model equations for wheat, compressed at 10-18% moisture content were calculated, and the relations between these parameters and wheat moisture were determined. It was found that the analyzed models described the pressure compaction of granular plant material with different accuracy, and were highly dependent on moisture. The study also indicated that the model of Ferrero et al. fits the experimental results well. The parameters of this model reflected very well the physical phenomena which occur during compression.