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Aiming at the problems of high labor intensity of weeding operations, the low weeding rate inter-plants and the seedling damage in transplanting rice field, a new method of weeding by water jet between plants in complex paddy filed environment was proposed. Based on the water jet weeding method and the mechanical structure design, a jet type inter-plant weeding device was designed. Firstly, by analyzing the structural characteristics of rice seedings, weed roots and submerged water jet, the injector angle was determined to be 31°and the diameter parameters of the injector was determined to be 0.004mm through theoretical analysis and parameter calculation. Combined with the momentum conservation theorem, the viscous fluid mechanics, and the soil mechanics analysis, the critical failure condition model of soil was established, and the critical pressure of earth breaking of the injector was obtained to be 0.53MPa. The extreme water pressure test of rice root system anti-breaking was carried out, and the maximum pressure limit of injector outlet was determined to be 1.5MPa. Besides, the bench test was carried out, the forward speed of the device and the pressure of the injector outlet were selected as the test factors, the weeding rate was used as the test index. Both the test index and the influencing factor regression model were established by using the method of secondary orthogonal rotation combination design. The Design-Expert 8.0.6 software was used to analyze and verify the test data, the results showed that when the forward speed of the device was 0.3m/s and the pressure was 1.5MPa, the weeding rate was 90.62%. The device can meet the agronomic and technical requirements of paddy field mechanical weeding operations.