The accurate magnetic properties of electrical steel sheets are important to develop high-efficiency electromagnetic devices. Especially, the H-coil method is a useful measurement technique of accurate magnetic field strength in single sheet tester. Therefore, we developed the tester of magnetic properties using the H-coil method, we called it the Stress load type - Single Sheet Tester (S-SST), and a problem was found in the iron loss measurement at high flux density, 1.6T or more. In this paper, it is shown that the cause of this problem is phase difference between induced voltage in H-coil and B-coil. In order that the phase difference make BH loop slightly twisted near the tip point, the iron losses are evaluated low. So, we propose the method of determining of phase correction values, these are measured in the absence of a specimen in the S-SST measurement system, and the phase correction method for induced voltage in a coil. Finally, the ideal results of correction on iron loss of non-oriented electrical steel sheets are shown. The proposed method is effective in calibration of a single sheet tester using the H-coil method.