【Objective】To improve the accuracy and reliability of automatic feeding rice seedlings in the orderly throwing transplanter, and reduce the seedling loss in the seedling feeding link. 【Method】A rice seedling-row-in-position detecting scheme and its practical program method were proposed，while a belt-type automatic seedling feeding mechanism (BASFM) and related control system were developed. Through prototype test, three kinds of characteristic signals representing the plug-seedling-row-in-position status were received based on direct-on-line detection of seedling stalk, plastic tray and magnetic bulge of ferric tray respectively. The synthetical measure attribute of plug-seedling-row-in-position signal was summarized. An optimal scheme to monitor plug-seedling-row-in-position and associated control circuit was established. The BASFM with functions of detecting seedling-row, transporting and feeding seedling was designed. 【Result】When body of plastic tray was chosen as a detected target, the success-detect rate was the highest (99.78%), magnetic bulges aside ferric tray was higher (96.64%) and seedling stalk was the lowest. When plastic tray or magnetic bulge of ferric tray was chosen as a row detected target, tray type showed no significant effect on success-detect rate, but significant while seedling stalk was chosen as a row detected target. For three seedling-row-in-position detecting schemes, the variance of transport motor speed also showed no significant impact on the seedling-row-in-position detecting performance between 30-60 r·min^-1.【Conclusion】This design of BASFM and affiliated seedling-row-in-position automatic detecting and control system can meet the performance requirements for pot-seedling-row transporting and feeding in the rice seedling orderly throwing transplanter.