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Keeping appropriate and consistent seeding depth and compaction pressure is beneficial to rapid and consistent seed germination, and finally increases yield. Seeding depth and compaction pressure varies with terrain floating and different field conditions. In order to make the planter adapt to varying field conditions and keep the seeding depth and compaction pressure in the set range, an electro-hydraulic precise control system for seeding depth and compaction pressure was designed, including hydraulic system, controller, downforce sensor, compaction pressure sensor, oil pressure sensor, and A/D signal acquisition modules. The downforce sensor and compaction pressure sensor were used to sense the real-time downforce and compaction pressure. Control signals were sent to hydraulic valves after calculating the differences between set value and actual measured value by controller, then the action direction and pressure of the hydraulic cylinder connected to the planter unit frame were adjusted, therefore the downforce and compaction pressure applied to the planter unit were adjusted. Through bench test, the control process of the system was calibrated. The step response test results of control system showed that the average adjustment time of the downforce control system was 2.69s, the average steady state error was 91.5N, and the average overshoot was 22.95%. The adjustment time of the compaction pressure control system was 1.44s, the stable state error was 30N and the overshoot was 1.83%. The mechanical spring-regulated seeding unit and electro-hydraulic-regulated seeding unit were installed on a same planter and their performances were obtained and compared though field tests. As for electro-hydraulic-regulated seeding unit, the seeding depth was set to 50mm, the target value of downforce was set to 3000N, and the target value of compaction pressure sensor was set to 400N. The planter operated at 6~10km/h. For the unit under electro-hydraulic active adjustment mode, the seed depth qualification rate was 91.33%, the coefficient of variation (CV) was 8.98%. For the unit under the mechanical adjustment mode, the seed depth qualification rate was 82.67%, and the CV was 16.73%. The test index of the unit based on the electro-hydraulic active adjustment method was better than the index of the unit based on the mechanical spring adjustment method. The research result provided a kind of electro-hydraulic method and system to adjust downforce and compaction pressure actively and accurately, which can finally realize consistent seeding depth and compaction pressure.