The invention discloses a clamping device of a clamp body of a long-tail clamp automatic assembling machine. The clamping device comprises a clamping mechanism and an ejecting mechanism. The clamping mechanism comprises an inverted T-shaped base platform, a slide which is formed by a left baffle, a right baffle, a front check block and a rear check block in a matching mode is fixedly arranged on the inverted T-shaped base platform, a clamp body base is arranged in the center of the slide, a left slide block and a right slide block are arranged on the left side and the right side of the clamp body base respectively, the end face in the middle of the left slide block and the end face in the middle of the right slide block are respectively provided with a through hole which is matched with a spring guide rod to be used, the spring guide rod penetrates through the through holes in the left slide block and the right slide block, and the two ends of the spring guide rod are connected with the front check block and the rear check block in a threaded mode. A spring is sleeved on the spring guide rod, and the end face of the lower right portion of the left slide block and the end face of the lower left portion of the right slide block are respectively provided with a first inclined plane. Second inclined planes matched with the first inclined planes are arranged on an ejecting push plate of the ejecting mechanism. The clamping device of the clamp body of the long-tail clamp automatic assembling machine achieves clamping of the clamp body of the long-tail clamp in the automatic assembling process, and greatly improves claming precision and clamping stability.