Abstract: Ultra-high pressure tubular reactor is widely used in polyethylene production in modern petrochemical industry. It is necessary to inspect the reactor regularly. Due to the change of the thickness of the remaining polyethylene powder layer on the inner surface of the reactor, the conventional eddy current test results will be interfered to a certain extent. In this paper, a differential probe was designed to detect the longitudinal cracks in the inner wall of the pipeline by pulsed eddy current method. Firstly, the eddy current distribution in the pipeline and the voltage signal of the received sensor were observed and analyzed by numerical simulation. It showed that the eddy current field generated by the designed longitudinal differential probe was disturbed by the longitudinal crack. And the received sensor could detect the corresponding signal at the crack location. Then the designed probe was used to carry out the detection test, the experimental results showed that the designed differential probe had a high sensitivity to the longitudinal crack detection of the inner wall of the pipeline. At the same time, the transverse probe was designed and the longitudinal crack was detected. The detection sensitivity of the longitudinal probe was much higher than that of the transverse probe. The proposed method had practical application value for the detection of longitudinal cracks in the inner wall of pipeline.