After the technical protection of relay protection overhaul, it is necessary to test the CT polarity and secondary circuit wiring for protection. The traditional inspection method is a one-pass method. The traditional one-pass method has the following problems: In the steady state mode, only the relationship between the polarities of multiple CTs can be checked, and the correctness of the polarity of a single CT cannot be judged. According to the principle, this paper analyzes the polarity of the secondary side of 500kV current transformer in 500kV substation and propose the plan design solution, which separates the primary side excitation power supply from the secondary side handheld terminal, so that the polarity detection effect is protected from the detection distance factor and the secondary side The signal acquisition system on the handheld terminal has been adjusted to enable it to successfully complete data collection in a variety of complex environments, greatly reducing equipment maintenance time and effectively protecting the operator"s personal safety. The feasibility and effectiveness of the detection technology were verified by conducting polar test analysis experiments on site. The field test results show that the detection system can accurately reflect the polarity error and is consistent with the theoretical analysis..