Abstract: Abstract: A precision rice hill-drop driller powered by a wheeled tractor will leave wide and deep wheel tracks in the field surface, which destroy the mud surface roughness and seriously affect sowing quality. A spiral filling approach with variable thread pitch and equal diameter was proposed in this paper. An opposed spiral filling device that is installed on a precision rice hill-drop drilling machine and powered by a Dongfanghong ME304 wheeled tractor was designed to solve the problem. When working in the field, the spiral filling assembly is powered through an independent hydraulic power system, and is driven by a hydraulic motor for rotation. The depth of the spiral blade into the mud is adjusted by the hydraulic lift rod through the tractor's three-point linkage. The rotating spiral blade pushes the surface mud in paddy field along the spiral axial to the wheel tracks that are formed by the tractor to eliminate the tracks. Taking soil particles as the research objects, stress analysis and motion analysis on soil particles were carried out in order to find kinetics and kinematics models during mud transportation process. The mathematical model was then established for the mud transportation capacity of the spiral filling assembly combing the tractor's working speed, parameters of tractor wheels, and automatic self-filling factor of the wheel track. The models helped for the determination of the spiral parameters. The spiral parameters were determined through the empirical formula of spiral design. Relationship curves between mud transportation speed and spiral radius and pitch were drawn with Matlab software to verify the rationality of the spiral parameters. After theoretical calculation and optimization design, key parameters of the spiral, the outer diameter, the inner diameter, and the maximum pitch were finally determined to be 250, 80 and 200 mm, respectively. The rotating speed of the spiral and the walking speed of the tractor should be adjusted according to the actual situation in the field. A spiral speed of 200 r/min and a tractor walking speed of 1 m/s were selected for field track filling tests based on the experimental field conditions in South China Agricultural University. Results show that with the tractor's automatic self-filling factor larger than 0.6, the spiral speed of 200 r/min and the tractor's forward speed no more than 1 m/s, the designed wheel track filling assembly is able to fill tracks of no deeper than 250 mm and less than 400 mm wide with smooth soil surface in order to provide excellent working environment for future sowing operations. The filling assembly has reasonable design and excellent operating performance. It is able to eliminate the wheel track and meet the actual production requirements. The study provides useful reference for further research and design of tractor track filling devices.