Due to the irregular shape of shrimp, the automatic orientation is difficult. In order to solve the problem that the orientation link of shrimp pretreatment still relies on manual operation and does not realize automatic operation, taking Penaeus vannamei as the research object, a shunting orientation method of abdomen and back for deheading shrimp was proposed. This method was a directional way of detection before sorting. In principle, it was different from the orientation method relying on friction and gravity. According to the principle that there were differences in the slope of the abdominal and dorsal curve of shrimp, the shunting orientation method of abdomen and back detected the ventral and dorsal orientation. Then the shrimp with different ventral and dorsal orientations were selected to achieve the same ventral and dorsal orientations. Theoretical analysis showed that the two-line photoelectric sensing method can be used to judge the ventral and dorsal orientation of shrimp. By controlling the transportation gap of shrimp, shrimp can be sorted, and finally the orientation of the abdomen and back of shrimp can be realized. According to the orientation method of abdomen and back for shrimp, the orientation system of abdomen and back for shrimp was designed, and the hardware construction and software development of the system were completed. The hardware of the system was mainly composed of photoelectric sensor, input and output module, computer and shunt mechanism. The test results of the detection accuracy and the orientation success rate showed that the average detection accuracy of large shrimp was 96.9% and the average detection accuracy of medium shrimp was 98.8%. And the average orientation success rate of large shrimp was 95.4% and the average orientation success rate of medium shrimp was 97.5%.