The exploition of the loose crop material needs compression process. To determine the structural parameters and optimize the design of compression equipment, the law of compression process, the relationship among main parameters in the whole compression process and the characteristerics of the material to be compressed are investigated. Based on the achievement acquired by our research group, a basic law of the stress and strain variation pattern was obtained by use of advanced measuring means, which provided a theoretical basis for the further study and optimum design of compression equipment.