Abstract: The field test was carried out by the test piece method, and the influence of polarization time, sampling delay time, sampling interval and the distance between sample and reference electrode on the test results of pipeline power-off potential of subway stray current interference in Suzhou area were discussed. The results showed that after cathodic polarization for 3 hours, the potential of the specimens with exposed areas of 6.5 cm² and 10 cm² tended to be stable. The power-off delay time should be no less than 100 ms. The power-off potentials of the two samples measured at the sampling time interval of 1 s and 2 s had little deviation. The larger the distance between the test piece and the reference electrode, the greater the fluctuation of the power-off potential deviation of the test piece. It was feasible to use portable reference electrode to test the cathodic protection potential of the test piece directly above the pipeline interferted by subway stray current interference.