A planting mechanism with planetary gears of transplanting machine was put forward. Its structure and working principle were expounded and motion trajectory equation was established. The characteristic coefficient λ was introduced and planting mechanism end’s motion trajectory was obtained with the different λ. Taking a single duck mouth planting mechanism as the research object, the virtual prototype was established, which was composed of planetary gears, seedling and the surface. The planting frequency of 30 plants/min was set as the design parameter. The former and latter duck mouth ends’ motion trajectory and the duck mouth’s opening, felling seedling situations were simulated when the λ was 0.90, 1.00, 1.18, 1.24 and 1.28. The simulation results showed that when λ was 0.90 and 1.00, the latter duck mouth avoiding seedling was not in time and making the seedling moving forward even lodging. When λ was 1.18 and 1.24, the former and the latter duck mouth avoiding seedling were full and the seedling wont be interfered. When λwas 1.28, the latter duck mouth avoiding seedlings’ space was more fully, but the former duck mouth avoiding seedlings’ space was insufficient and the seedling was interfered. When the characteristic coefficient λwas 0.90, 1.00 and 1.22, the prototype experiment was carried out on cucumber seedling of 20 d in the homemade soil bin. The results showed that for λ of 1.22, the upright degree of seedling was the best. The excellent-good rate was up to 86.7%. For λ of 0.90, the upright degree of seedling was the worst and the excellent-good rate was 0. The test results and simulation results were consistent.