Abstract: The calculation of pipeline cathodic protection range and protection current requirement is an important part during the design procedure of cathodic protection. Aiming at the problems in the calculation formulas in existing standards, the pipeline attenuation formula was deduced based on transmission line theory. Through the attenuation formula, the physical meaning of key parameters for the calculation of cathodic protection range was clarified, and the error sources of the existing calculation formulas were studied. Furthermore, a new calculation formula was proposed, which had higher accuracy than the traditional one.