Aiming at the problems of poor soil-stone separation effect, high soil content rate, high stone leakage rate and poor machine adaptability of farmland stone picker under sandy soil conditions in Northwest China, a hydraulically driven chain-type farmland stone picker was designed, which can complete the picking, conveying and collecting of stones in the tillage layer at one time. Through the optimized design and theoretical analysis of key components such as the soil entry device and conveying separation device, the relevant structural parameters were determined. The motion analysis of stones in the conveying device was focused on, and the motion models of stone conveying in different stages were constructed. The collision of soil-stone mixture in the reflux process was used to increase the fragmentation degree of soil attached to the stone surface and soil blocks, so as to improve the separation efficiency. Through DEM MBD co-simulation, the simulation model of soil and stone conveying was established. Taking the operating speed, the spindle speed of the conveyor chain and the separation stroke of the conveyor chain as the test factors, and the stone leakage rate and soil content rate as the test indexes, the single-factor simulation test was carried out to determine the optimal interval range of each factor. Taking this interval as the factor range, the quadratic orthogonal simulation test was further carried out to obtain the optimal working parameter combination. The results showed that when the machine operating speed was 0.7 m/s, the spindle speed of the conveyor chain was 110 r/min, and the separation stroke of the conveyor chain was 2 700 mm, the performance was optimal, the stone leakage rate was 8.22%, and the soil content rate was 2.58%. Under the optimal parameter combination, the field verification test was carried out, and the stone leakage rate was 8.03% and the soil content rate was 2.62%, which met the national standards and industry requirements.