Traditional classification method for crab by artificial to distinguish its gender and by eyes to estimate its weight, so the classification efficiency and accuracy are lower. The gender identification base on image recognition technology is implemented with the LABVIEW software platform. The identification result is transmitted to the S7-200 controller by OPC communication technology, at the same time the weight of the calibration of crab is implemented by weighing sensor. The control system of automatic classification is finally implemented with the classification indexes of weight and gender, the recognition accuracy of this system is about 95%.