Abstract: The bale stability affects its quality. Nowadays, some problems exist in cubic bale that formatted in baler——the geometrical instability, the bale scattered before using or bale size varied in a wide range. Hay under compressing has shown that the formation of wafers is a material deformation phenomenon, governed by such properties of the material as viscoelasticity. Based on viscoelastic consideration from the observation, the total deformation has both recoverable and irrecoverable components, the recoverable deformation associated with recoverable force have relationships with bale density and stress relaxation. Unstable recovery of bale originates in diverse recoverable force. Mathematical model was established to investigate the influence of recoverable force and stress relaxation by applying rheological theory in cubic bale production. Principles of recoverable force as well as stress relaxation in the compression were discussed in the paper, the difference between the upper section and the lower one due to uneven feeding shows great influence on bale stability. It is essential for both baler design and practical production.