Abstract: Single sheet tester is conventional equipment for measuring the magnetic properties of electrical steel, the measurement methods have been well defined by the national standard GB/T 13789-2008 (IDT IEC 60404-3:2002) “Methods of measurement of the magnetic properties of magnetic sheet and strip by means of a single sheet tester”. With the development of new high-grade products with domain refinement, thin gauge, and low losses, the requirements for the performance of measurement equipment continue to increase, and the additional losses generated by the yoke of the single sheet tester during actual measurement is a problem that cannot be ignored. The current national standards only point out that the yoke should be made with low and constant losses, but no specific treatment is required for the additional losses generated by the yoke. This paper studied the measuring method of the loss generated by the yoke of a single sheet tester and analyzed its effect on the measuring result of the magnetic properties of electrical steel based on the data of yoke loss for different points of magnetic polarization, the method of deducting the yoke loss is given accordingly.