Abstract: Investigation found that the potential of feeding point was higher than the set potential of potentiostat in Gaotang CP Point of ZhongCang Gas Transmission Pipeline. There was no defect probability in CP system itself proved by relative inspection. Analysis on the measuring process of feeding point showed that different electric intensity between the long-term reference electrode and the potable reference electrode resulted in the ΔU between the potential of feeding point and the set potential from potentiostat. Practice proved that if the long-term reference electrode of potentiostat was connected into the test box of feeding point potential and a benchmark zero was adopted by the long-term reference electrode and the potable reference electrode, the ΔU would be completely eliminated.