Abstract: Dynamic simulation technique has been applied to agricultural machinery design. The simulation was based on the models of system and its operating objects. Modeling of matured crops and the operating objects of harvesting machine were studied． The Mathematical model of field distribution of growing matured crops was built with the method of stochastic process and plural statistical analysis to describe the field distribution of crops (including stems, ears, grains). This model can be used to build the mutual action between crops and striper in harvesting operation.