In the deep sea, direct measurement of pipeline cathodic protection status is very difficult. We explored a noncontact method by measuring the potential distribution of the environment field around the undersea pipelines to detect the rotted points on the coating surface. It included two aspects: developing a new type of the solidstate Ag / AgCl reference electrode for the deep sea; useing the virtual instruments to design the environment field measurement system. The noncontact measurement system was applied in the ocean of Qingdao city, P.R.China as experiments. The experimental results show that the noncontact measurement system within four meter distance to the undersea pipelines, can accurately detect rotted points.