The direct current voltage gradient method (DCVG) is an indirect measurement method used to evaluate defects in anti-corrosion coatings of pipeline. The implementation of DCVG detection has certain requirements for the DC test current and the setting of interrupters, but these technical details are often ignored in actual on-site work. %IR is a parameter used in the DCVG method to evaluate the severity of pipeline coating damage. There are many misconceptions in the calculation and application of this parameter in the pipeline industry, such as the incorrect selection of the test current and on-off period, and lack of consideration of factors such as soil resistivity and burial depth of the pipe. This article has conducted research and discussion on the testing current requirements of DCVG and the principle and calculation method of %IR, clarified the signal strength requirements for conducting DCVG inspection, analyzed the factors that affect the %IR value, and pointed out that it's uncertain to evaluate the size and severity of coating defects using %IR.