The present invention provides a pot seedling feeding system for a transplanter, including a conveyor unit, a detection sensor, a controller, a seedling separation unit, side plates, and support stands. The conveyor unit includes a step motor, a transmission shaft, a conveyor belt, a tensioning shaft, and bearings. The seedling separation unit includes a seedling separation rod, a reset spring, a guide post, and a support seat. The controller is used to control the step motor which drives the conveyor belt in order to move the pot seedling. When a seedling receiving barrel of the planter rises to a seedling receiving position, the planter is controlled by using a brake cable, the seedling separation rod is then ejected which in turn drives the step motor to carry a pot seedling to move forward. The pot seedling is then dropped in a seedling receiving cup of the planter. In order to improve the quality of pot seedling planting, the seedling separation rod corrects a feeding posture of the pot seedling at the moment when the pot seedling drops. The present invention is about a mechanical seedling feeding system adopting the conveyor unit and the seedling separation unit that move intermittently, where multiple pot seedlings can be placed at a time, so that the operation is simple and fast, labor is saved and the cost is reduced. Stress from missing seedlings and excessive fatigue from repetitive movement are also eliminated from the implementation of this device.