Aiming to achieve orderly seeding of giant Juncao seed stems, enhance seeding efficiency and accuracy, and prevent damage to seed buds, a reciprocating roller precision seed dispenser for giant Juncao seed was designed. This device consisted of a reciprocating seed feeding mechanism, a roller seed dispensing mechanism, and seed guiding components. Based on the physical characteristics of giant Juncao seed stems in the Northwest region and the agronomic requirements for planting the stems, theoretical analyses were conducted on the processes of seed feeding, dispensing, and output of the device to determine the structures and parameters of key components. The working process of the seed dispenser was simulated by using the EDEM method to analyze the forces and motions acting on the stems, confirming that no damage occurred during the seed feeding phase. Using seed filling rate, clogging rate, and qualified planting distance as experimental indicators, a second-order regression orthogonal rotary combination simulation experiment was designed. The optimal structural parameter combination for the seed dispensing roller was determined to be: groove depth of 16 mm, groove width of 24 mm, and surface spacing of 7 mm. The optimal structural parameters for the seed output port were as follows: side plate inclination angle of 45°, opening width of 45 mm, and opening length of 30 mm. To determine the best operational parameters for the seed dispenser, the qualified planting distance rate and the variation coefficient of planting distance were used as experimental factors in a second-order regression orthogonal rotary combination test. The results showed that when the rotation speed of the seed dispensing roller was 11.57 r/min, the height from the seed discharge port to the ground was 191.56 mm, and the inclination angle was 35.77°, the qualified planting distance rate reached 96.4%, with a variation coefficient of 9.98%. The working performance of the seed dispenser met the agronomic requirements for giant reed planting.