An off-line calibration platform is designed based on the requirement of off-line calibration of induction cavity azimuthal transmission line current probe. The analog device is a flat-plate transmission line structure, which has lower distortion than on-line calibration. The source of cross-platform calibration error is analyzed, and the measures to reduce the error are put forward. The analysis shows that the installation eccentricity and probe longitudinal installation depth are the biggest sources of cross-platform calibration error, which need to be paid attention to in engineering design. An off-line calibration platform is established and the error analysis is carried out. As a result, 3.3% cross-platform calibration error is obtained.