Provided is a conservation of momentum presentation device. The conservation of momentum presentation device comprises a first semi-circle slot, a second semi-circle slot, a support pillar, a falling sphere pool and a metal ball. Threaded holes are arranged at four corners of a base and screws which are matched with the threaded holes are also arranged at the four corners of the base. The first semi-circle slot is beset on the bottom edge of the base; the falling sphere is fixedly connected with the right end of the base, the second semi-circle slot and the first semi-circle slot are fixedly connected in a slidable mode. The left end of the second semi-circle slot is fixedly connected with the upper surface of the base through the support pillar. The diameter of the metal ball is smaller than the inner diameter of the first semi-circle slot. The distance from an axis line of the first semi-circle slot to two lateral faces of the front base and the back base is equal. The screws are revolved and the base is adjusted to the level, six metal balls are put into the first semi-circle slot side by side, seven metal balls are put into the left end of the second semi-circle slot and then hands are loosened. The metal balls are rolled down and an elastic collision between the six metals balls and the metal balls at the left end of the first semi-circle slot happens and then keeps still. Finally, the metal balls at the extreme right end of the first semi-circle slot are bounced out and fallen into the falling sphere pool, other metal balls keep still. The conservation of momentum presentation device has the advantages of being simple, convenient and practical, obvious in effects.