The invention discloses a third folding device of a linen folding machine. The third folding device comprises a first conveying roller set, a second conveying roller set and an inserting plate mechanism, roll shafts at the two ends of each second feeding conveying roller are fixedly connected with a machine frame, roll shafts at the two ends of each first feeding conveying roller are connected with one ends of connecting rods respectively, the other ends of the connecting rods are hinged to the machine frame, and the roll shafts at the two ends of each first feeding conveying roller are connected with the machine frame through elastic connecting devices, so that when the first feeding conveying rollers are squeezed by an inserting plate, the first feeding conveying rollers rotate towards the outer sides of the second feeding conveying rollers to avoid the inserting plate. The third folding device has the advantages that the inserting plate can be inserted into and pulled out of a feeding inlet of the third folding device conveniently, damage of linen or the feeding conveying rollers can be effectively avoided, and when linen is clamped in the feeding inlet of the third folding device, linen can be conveniently taken out and can not be damaged.