To analyze the influence of the special structure of common-phase parallel cables on distance protection, the sequence equivalent model of double-circuit parallel cable is established and the analytical expressions of the measured impedance are derived. The main factors affecting the performance of distance protection are analyzed, and the calculation methods of the minimum range of first-zone distance protection and maximum measured impedance are given. The correctness of the analysis conclusion is verified by digital simulation. Results show that the measured impedance of grounding impedance relays and phase-to-phase impedance relays will increase because of the special structure of common-phase parallel cables. This will reduce the protection range of first-zone distance protection and the sensitivity of second-zone distance protection. This needs attention in the calculation of relevant protection settings to ensure the safety of cables. This work is supported by National Key Research and Development Program of China (No. 2016YFB0900600).