Abstract: Melilotus offcinalis is an alien invasive plant widely distributed in China, which poses a serious threat to the biodiversity of the invasive areas. The characteristics of reproductive structures and seed germination of M. offcinalis were studied based on quadrat investigation and seed germination experiment. The results showed that density had different effects on the characteristics of reproductive structures of M. offcinalis. The number of seeds per branch, total number of seeds and 100-seed weight were inversely proportional to density, while the branch number reached the maximum at medium density, and the plant height and branch number at high density and low density were lower than those at medium density. And, there was a significant positive correlation between total seed quantity and single branch seed quantity（r=0.946）, and a significant positive correlation between 100-seed weight and single branch seed quantity（r=0.178）. In terms of germination characteristics, cold storage promoted the germination of M. offcinalis seeds, increasing the germination rate by about 10%, while cold storage inhibited the germination of M. offcinalis seeds, decreasing the germination rate by about 30%. At room temperature, the dormancy characteristics of M. offcinalis seeds fluctuated greatly in the first 7 months, and remained stable from 7 to 20 months. The germination rate kept about 80%, then gradually decreased, and decreased to less than 10% after 5 years. The results showed that melilotus melilotus had higher seed yield and higher germination rate, which was beneficial to its population diffusion and colonization.Melilotus offcinalis is an alien invasive plant widely distributed in China, which poses a serious threat to the biodiversity of the invasive areas. The characteristics of reproductive structures and seed germination of M. offcinalis were studied based on quadrat investigation and seed germination experiment. The results showed that density had different effects on the characteristics of reproductive structures of M. offcinalis. The number of seeds per branch, total number of seeds and 100-seed weight were inversely proportional to density, while the branch number reached the maximum at medium density, and the plant height and branch number at high density and low density were lower than those at medium density. And, there was a significant positive correlation between total seed quantity and single branch seed quantity（r=0.946）, and a significant positive correlation between 100-seed weight and single branch seed quantity（r=0.178）. In terms of germination characteristics, cold storage promoted the germination of M. offcinalis seeds, increasing the germination rate by about 10%, while cold storage inhibited the germination of M. offcinalis seeds, decreasing the germination rate by about 30%. At room temperature, the dormancy characteristics of M. offcinalis seeds fluctuated greatly in the first 7 months, and remained stable from 7 to 20 months. The germination rate kept about 80%, then gradually decreased, and decreased to less than 10% after 5 years. The results showed that melilotus melilotus had higher seed yield and higher germination rate, which was beneficial to its population diffusion and colonization.