A kind of transplanting seedling disc conveying device and positioning control system were developed for automatic disk conveying and accurate position of pot seedling transplanter. The moving speed and distance of seedling disc could be adjusted according to the disc size, which was driven by gas-liquid damping cylinder. The PLC was used as control core and the touch screen was used as human-machine interface. Experimental results showed that the influence caused by the cylinder response lag and machining error could be eliminated by setting the compensation value. The positioning control error was less than 1mm, which met requirements of high-speed automatic transplanting machine.