In view of the problems such as the lack of deep planting mode and harvesting equipment for scallions on flat land in Qinghai region, as well as the high cost and low efficiency of manual harvesting, a crawler self-propelled cross-row scallion harvester was designed. This machine integrated multiple functions such as depth limit excavation, clamping and conveying, and orderly laying, and can complete the operations of trenching, scallion excavation, conveying and collecting in one go. Low-resistance harvesting was achieved by using a U-shaped plough for soil breaking and excavation structure in combination with a rotating knife group for trenching. The overall passability and stability of the machine were enhanced through a hydraulic drive system. The parameters of the hydraulic system were matched and optimized, and the selection and design of the hydraulic motor and variable pump were completed. Meanwhile, the flow-pressure characteristic tests of the hydraulic pump and the flow characteristic tests of the hydraulic motor were carried out. Performance tests showed that under the start-up and high-load conditions of the harvester, the flow rate and pressure of the hydraulic pump and the flow rate of the hydraulic motor all underwent sudden changes, and then entered a stable state, indicating that the system provided stable energy supply, responded quickly, and had a good pump-motor matching, which can adapt to different high-altitude working conditions. The results of field trials showed that the net working efficiency of this machine was 0.35 hm2/h, the damage rate was 1.22%, the loss rate was 0.81%, the success rate of loading and unloading was 98.63%, and the effective excavation rate was 97.84%. All indicators were superior to the industry standards, verifying the structural feasibility and adaptability of this machine, and providing technical support and equipment foundation for the mechanization of scallion harvesting in plateau areas.