Abstract: In order to make rational use of corn straw, the whole plant of corn straw in cold region was collected. Combined with self-made experimental device, the mechanical properties of different diameter parts of corn straw at the same loading rate, segmental radial and axial compression and no segment bending were tested by electronic universal testing machine. The experimental data are fitted and the related mathematical models are established. The results show that when the diameter is less than 20mm, the effect of diameter on pressure is not obvious in the axial compression experiment, when the diameter reaches about 25mm, the effect begins to appear, and the effect is very significant when the diameter is larger than 29mm. During radial compression, the diameter of several segments near the top of straw is approximately linear with the pressure, but with the increase of diameter, the radial pressure does not rise in the mean value, so it is discrete to a certain extent. In the bending test, in the initial stage, the pressure fluctuates up and down in a certain range, and the diameter has no significant effect on the pressure; when the diameter is larger than 23mm, the required pressure value increases significantly; when the diameter is larger than 30mm, the influence of diameter on pressure fluctuates obviously. The experimental data are true and reliable, and the fitting results have strong referability, which provides a theoretical basis for better development and utilization of straw resources and better optimization of straw harvesting device structure.