In order to study the mechanism and its effect on germination and emergence of inner mechanical cracks of corn seed kernels in threshing, a computer recognition system of corn seed mechanical damage was developed and low damage corn seed threshing principle and device parameters was analyzed. The typical external characteristics of corn seed, distribution of crack, formation rule of inner mechanical crack and damage extent were studied by means of stereomicroscope technical method. Distribution and formation regularity of corn seed mechanical cracks were explored. The result showed that obvious differences universally existed in shape and size and the inner mechanical cracks of three kinds of corn seeds, the long cracks were accounted to 39.8% of cracks damage. The main reason for inner crack formation was that crown of corn kernel was shocked by the threshing parts while feeding. The cracks started from the impacted area of corn kernel crown and enlarged to the embryo inside crown. The information about the inner cracks could be found from the crown and back of corn seed kernel.