The invention provides a tooth grinding tool for internal spline gears, which includes a tooth grinding mandrel, a first nut, an elastic metal ring, an expansion sleeve and a second nut. The shank, the first external thread section, the tapered section and the second external thread section, the tapered section is small in front and large in the rear, the first nut is screwed on the first external thread section, a tapered hole is arranged in the expansion sleeve, and the expansion sleeve Located on the tapered section, the outer wall of the expansion sleeve is arranged with a plurality of spline teeth, the outer surface of the expansion sleeve is arranged with a plurality of through grooves, and the side wall of the expansion sleeve is also provided with a first opening. Filled with sponge, the sponge is impregnated with lubricating oil, the second nut is screwed on the second external thread segment, the elastic metal ring is provided with a second opening, the elastic metal ring includes multiple convex plates, and the multiple convex plates pass through the screw It is fixedly connected to the rear end face of the expansion sleeve. Due to the adoption of the above technical solution, the present invention can improve the fixing stability and the machining accuracy of the internal spline gear.