Device and method for measuring diameter size of inner end surface of casing

The invention discloses a device and a method for measuring the diameter size of the inner end surface of a casing. The measuring device comprises a device body, a movable measuring head, a fixed measuring head, a measuring meter, a meter base and a connecting structure, the movable measuring head is arranged at the first end of the device body and is used for moving along the axial direction of the device body to abut against the inner end face of the casing, the fixed measuring head is arranged at the second end of the device body and is used for abutting against the inner end surface of thecasing, the measuring meter is used for measuring the displacement of the movable measuring head, the meter base is arranged on the device body and is used for installing the measuring meter, and theconnecting structure is arranged on the meter base and is used for connecting the movable measuring head and the measuring meter; the device body is arranged on the inner bottom surface of the casing, and allows a connecting