To realize the auto-pick up of plug seedlings by 2Y–2 type semi-auto transplanter, an auto plug seedling pick-up mechanism constituted with sector gear, grooved cam and retractable seedling clip is designed. As the wheel hub-shaped grooved cam influences the motion trajectory, main structural parameters including the law of motion, center-to-center spacing, the length of swing rod and polar radius were designed and calculated. And orthogonal test was applied on the depth reached, the installing angle, the moisture content of the matrix and the rotational speed which influence seedling picking of the mechanism. The results showed that when the depth of the seedlings is 34 mm, the angle is 75°, the moisture content of the matrix is 22% and the rotational speed is 18 r/min, the amount of matrix falling off the plug seedlings, the total length of the broken roots and the seedling leakage rate all reached the minimum.