The invention relates to a one-way seal ring for pump in coal chemical industry and belongs to coal chemical industry field. The one-way seal ring comprises a variant ring and a locating ring, wherein the variant ring is processed by elastic materials, and the locating ring is processed by hard materials. The variant ring at free status is in the same structure as the locating ring. Both the variant ring and the locating ring are in forward convergence cone structure. The outer edge of the rear end of the cone structure extends outwards to form a circular junction board. The variant ring and the locating ring are glued and fixed throng the respective circular junction board to form a conical assembled unit. The circular junction board of the one-way seal ring is fixed on the outer wall of a ring pipe to be sealed. The inner hole of the variant ring at the front end of the one-way seal ring is interference fit on the inner wall of the ring pipe to be sealed. The inner hole of the locating ring at the rear end of the one-way seal ring is clearance fit with the side wall of a mechanical seal short sleeve. The one-way seal ring has the advantages of simple structure, convenient installation and reliable seal and cooling effect. A One-way passage is formed by a pump cavity and mechanical seal cavity. The invention has important application value.