Abstract: In order to reasonable use a space resource, and improve the seed yield of Onobrychis viciaefolia. Experiment with the material of Qitai Onobrychis viciaefolia, by setting different planting density. The relationship of planting density on seed yield of Onobrychis viciaefolia that was researched by plant height, branches of plant, number of pod, 1000-grain weight and seed yield. The results showed that, the density of 30 cm×25 cm was better than others. The inflorescence number of plant, number of pod, 1000-grain weight and seed yield were 81.1, 839.2, 23.8 g and 1995.8 kg/hm². Relevance analysis showed that, the seed yield and 1000-grain weight had significant correlation 0.631; the seed yield and the number of pod correlation coefficient was above 0.998.