The longitudinal intermittent precise delivery of soft seedling trays is a prerequisite for precise transplanting of rice seedlings by a seedling transplanter. Aiming at the problems of rigid impact and unsatisfactory self-locking effect in the existing cam-type intermittent feeding device, a gear-linkage-shaped-slot-wheel combination longitudinal precise feeding device with a flexible impact characteristic was proposed. The kinematic model of the shaped-slot wheel mechanism was established, and the characteristics of angular velocity and angular acceleration of the slot wheel during movement were analyzed. Based on the minimum rewinding radius of the seed tray, the number of slots, movement and stop times of the slot wheel were determined. A pair of double circular pins was introduced to solve the overshooting problem of the slot wheel caused by inertia during rapid rotation. An end face braking mechanism was used to eliminate the accumulated error in the rotational angle of the driving gear due to its inertia, so as to achieve precise intermittent motion of the feeding device. The spring preload force was determined through calculation. Finally, a two-row seed tray box suitable for seedling transplanting was developed, a test bench was manufactured, the angular deviation of the device was measured, and a longitudinal seed harvesting test was conducted. The test results showed that the single longitudinal feeding angular deviation of the device was within the range of -1.5° to 1.8°, and no error accumulation occurred during seed harvesting. By matching the seed harvesting test bench with the transplanting mechanism, accurate seed supply and clamping and pulling of seedlings can be achieved, i. e. , the longitudinal seed harvesting device design met the operational requirements.