The utility model relates to a grouting device for seams of an underground diaphragm wall. The grouting device consists of two shock tubes, dense screens and a plurality of steel tubes, wherein the two shock tubes are transversely communicated through the steel tubes; each shock tube is wrapped by the corresponding dense screen and then is welded at each of the seams on two sides of a reinforcement cage of the underground diaphragm wall in advance; if the seams of the underground diaphragm wall leak in a later period, the two shock tubes of the grouting device can be directly utilized for double-liquid grouting plugging; if the seams do not leak, the two shock tubes of the grouting device are plugged by cement slurry. The grouting device for the seams of the underground diaphragm wall has the advantages of high treatment efficiency and low cost, the seams are plugged from the interior of a wall body, the effect is remarkable, and the problem of leakage of the seams of the underground diaphragm wall can be effectively solved.