Aiming at the current situation of lack of relevant standards and performance testing devices for anti-DC transformers, and combining with the traditional transformer calibration method, a digital direct calibration method without standard transformer is proposed. Through the analysis of the existing standard and the use of half-wave current, this paper presents the error limit of anti-DC transformer under half-wave current. Through the spectrum analysis, the transmission characteristics of anti-DC and traditional electromagnetic transformers under half-wave current are obtained. In order to reduce the influence of spectrum leakage, the windowing interpolation Fourier analysis algorithm is used to calculate the ratio difference, and the relevant amendments are derived. The hardware and software design of the test system and the prototype development are carried out. Experimental results show that this method can improve the reliability of the test system and has good stability, operability and practicability. This work is supported by Youth Fund of National Natural Science Foundation of China (No. 51307066).