A key cup adjustment device for a wind instrument has a hinge rod and a key cup assembly. The key cup assembly is mounted on the hinge rod and has at least one solid arm, a key cup, at least one adjusting arm and at least one abutting unit. The at least one solid arm is mounted securely between the hinge rod and the key cup. The at least one adjusting arm is mounted securely on the at least one solid arm and corresponds to the key cup. The at least one abutting unit is connected to the at least one adjusting arm and can be adjusted to abut the key cup. Therefore, the key cup can close a corresponding tone hole tightly and pitches produced by wind instruments are accurate.