Compression deformation at room temperature of medium carbon cold heading steel SWRCH45K was conducted by universal testing machine, the surface and internal microstructures of compression samples were observed, and the axial strain and circumferential strain at the equator position on the side surface of compression samples were analyzed. The results show that in the compression deformation process, firstly the compression load increases steadily with the increase of displacement, when the displacement is greater than 7.5 mm, it increases rapidly, and the drumshape value of compression samples first increases and then decreases with the increase of displacement. When the displacement is 7.5 mm, the changes in trends occur simultaneously. The reason for this phenomenon is regarded as the uneven strain hardening of compression deformation. When the compression deformation under the condition of the displacement less than 7.5 mm, the large forming region is located at the center of the compression sample, and the strain hardening is relatively large. While in subsequent compression deformation of the displacement greater than 7.5 mm, it no longer is the maximum forming region due to high strain hardening and large deformation force to deform further, and the increase in the degree of strain hardening is reduced. On the contrary, the large deformation is produced at the previous difficult deformation region and small forming region due to the lower strain hardening and deformation force to deform further,and the increase in the degree of strain hardening is improved significantly.