Based on the transient signal wavelet entropies, a novel non-unit transient protection principle appropriate for transmission-line single-phase-earth faults was proposed in this paper. The wavelet entropies were normalized according to the transition impedance and fault initial angle before the construction of the protection criterion, so that the effects of both transition impedance and fault initial angle on the line protection could be eliminated. In the protection scheme, the normalized wavelet entropy was defined as the fault characteristic variable, and it had the function of value comparison. Thus, the reliability of protection was greatly improved. Its validity has been extensively tested by the simulation of different varieties of faults on a 500 kV power system modelled in ATP/EMTP.