The utility model relates to a positioner of large -scale speed reducer box, the device be equipped with be used for the speed reducer box along horizontal plane X to and Z to the dumbbell round pin of location, the last box of speed reducer with be equipped with the dumbbell pinhole down between the box faying face, the setting is sold in the dumbbell pinhole to the dumbbell, the dumbbell is sold and comprises middle cylinder, tip cylinder I and tip cylinder II, and tip cylinder I is fixed respectively with tip cylinder II and is set up at middle cylindrical both ends, and the diameter of section of tip cylinder I and tip cylinder II all is greater than middle cylindrical diameter of section, the utility model discloses a structure of dumbbell round pin, processing dumbbell pinhole on the faying face of box, in the middle of the dumbbell round pin face of cylinder play box horizontal plane X to the location, length and size between the face cylinder of both ends and the size of box dumbbell pinhole are matchd, play box horizontal plane Z to the location, cylindrical length and size in the middle of the dumbbell round pin only need singly be joined in marriage to the course of working, has reduced the processing degree of difficulty of box, has improved work efficiency.