The invention discloses an adjustable auxiliary device for a shore hardness tester rack. The device comprises a base body with a cavity, a fixing part and an insertion assembly, wherein a boss with a through hole is arranged in the cavity in a bulging manner; the fixing part comprises a cylinder connected with the base body, an arc fixing body connected with the cylinder, an adjusting pillar fixed at one end of the arc fixing body and an adjusting block sliding relative to the adjusting pillar; the insertion assembly comprises an inserting rod, a connecting rod and a pushing rod, the connecting rod is hinged with the inserting rod and the pushing rod respectively, the inserting rod penetrates through the through hole and slides relative to the through hole, an accommodating groove is formed in the inserting rod, one end of an elastic bulged bar is fixedly connected with one side wall of the accommodating groove, the other end of the elastic bulged bar is a free end bulged out of the inserting rod, the pushing rod and the inserting rod are perpendicularly arranged, and the pushing rod can slide relative to the base body. By means of the auxiliary device, cylindrical parts with different diameters can be stably placed on the surface of a base of the shore hardness tester rack, and accordingly, the testing result is more accurate.