By analyzing two-kind differential current（DC） such as: DC with delta-star and with star-delta connection used for second harmonic magnetic inrush current restrained， it shows that the former has no advantage over the later on identifying the inrush， and the decreasing situation of second harmonic is existing in transformation process. In addition， because wrong act may occur when transformer energized， split-phase blocking should not be adopted. A new sample current method for effectively judging the magnetic inrush currents is proposed， it can realize single-phase braking， improve reliability of inrush current blocking and no-load fault sensitivity of magnetic inrush current restraint for transformer differential protection. The new method shows higher sensitivity and reliability than that of other differential current， which is proved by more than 10 000 groups of batch experimental simulation data and field no-load energized examples.