Based on double Epstein frame measurement method, double Epstein frame measurement experiments are carried out for 30P120 silicon steel samples using two pairs of Epstein frames (namely 2E (25-20) and 2E (20-17.5)) magnetic measuring devices, to study factors affecting the mean path length of the Epstein frame. 3D simulation proves the preconditions of double Epstein frame method, that is equivalent magnetic flux density of corresponding corner positions. On this basis, a weighted processing method is proposed to determine the effective path length of standard 25cm Epstein frame and to compare with that of double Epstein frame method, which processes the mean path length determined by the different specific losses of the Epstein frame (i.e., the uniform areas, the corner areas and the impact zones between them of the whole Epstein frame). Not only the method excludes the effect of the magnetic characteristics inhomogeneity of samples in the corner double-lapped structure areas, but also considers the influence of the specific power losses in the different parts determining the mean path length. The obtained experimental results confirm the correctness of the method in this paper for determining the specific total loss of electrical steel sheet.