The invention relates to the technical field of inner star wheel tools, and discloses an inner star wheel ball assembling device. The device comprises a push rod, an outer conical part, a clamping jaw, an external pressing part, an outer sleeve and an elastic part; the outer conical part is arranged at one end of the push rod, and comprises an outer conical portion, the diameter, in the directionaway from the push rod, of the outer conical portion is gradually increased, the clamping jaw is arranged on the periphery of the outer conical portion, the external pressing part is arranged on the push rod in a sleeving manner, and can slide relative to the push rod, the inner wall of the external pressing part is provided with an inner conical portion matched with the outer conical portion, theouter sleeve is arranged outside the push rod in a sleeving manner, and can slide relative to the push rod, one end of the clamping jaw can stretch out of or retract into the outer sleeve, the elastic part is arranged on the push rod in a sleeving manner, abut-pressing portions are arranged on the push rod and the outer sleeve, and the elastic part is located between the two abut-pressing portions. A ball between an inner star wheel and an outer star wheel can be rapidly mounted, mounting accuracy is ensured, and life safety of a worker is ensured.