Aiming at the calibration traceability problem of barrel’s inner diameter instrument, the structure principle of barrel’s inner diameter instrument is expounded. The principle and composition of calibration device with double dynamic measuring heads is designed. The measuring model is founded. The main factors affecting calibration result are analyzed and the affection by each factor is evaluated. Finally, the uncertainty is presented. The results show that the uncertainty of calibration device is 0.43μm, the calibration result’s uncertainty of inner diameter instrument is 2.9μm. The calibration traceability requirements can be meet and the automatic calibration is realized.