The invention discloses a field calibration instrument for a flange. The field calibration instrument comprises a main matching body, a steel shaft, a pointer regulator, a steel sleeve, a bearing, a dial, a pointer and an infrared ray emission assembly. The bearing is arranged in the main matching body, one end of the bearing is tightly attached to the inner wall of the main matching body, and thedial is arranged at the other end of the bearing; the steel shaft penetrates through a rolling shaft and the dial in sequence and is connected with one end of the pointer regulator, the other end ofthe pointer regulator is connected with the steel sleeve, and the pointer is arranged on the pointer regulator. The main matching body, the steel shaft, the pointer regulator, the steel sleeve, the bearing and the dial are coaxial, and the infrared rays emitted by the infrared ray emission assembly come out from the axis. When flange pipe calibration is conducted through the field calibration instrument, the operation is simple, no technical requirements for operators exist, the work efficiency and accuracy are improved, and the field calibration instrument is easy to apply and popularize.