The equal-diameter cam seedling-pushing mechanism was proposed in order to solve the problem that the structure size of conjugate cam seedling-pushing mechanism was too big. In the proposed seedling-pushing mechanism, equal-diameter cam was used to control the motion of seedling-pushing rod. Ideal kinematic curves of seedling-pushing rod were constructed and reverse model of the proposed seedling-pushing mechanism was established according to requirements of planting agriculture as well as driving mechanism with planetary elliptic-gear trains. Then a reverse design and simulation software was compiled based on VB 6.0. A set of optimum parameters including structural parameters as well as pitch curve of equal-diameter cam were obtained through the software, which could meet the requirements of planting agriculture. The seedling-pushing mechanism was developed based on these parameters and testified by high-speed video. Analysis and results of the experiments showed that the proposed seedling-pushing mechanism could meet the requirements of planting agriculture and had a smaller outer dimension compared to conjugate cam seedling-pushing mechanism. 