Abstract:Alfalfa is a high quality perennial leguminous grass. Weeds in seedling stage often cause serious reduction of product or even a failure. Experiments on chemical control of weeds in sunlight greenhouse, big plastic shed, waste slope land and basic farmland were carried out. Results show that either application of herbicide in the soil before sowing, or spraying over the soil surface after sowing, or stem and leaf treatment after sprouting can control the harm of weeds effectively in alfalfa field.