Abstract: The traditional distance protection is no longer applicable to the half-wavelength AC transmission line for the completely different characteristics from the conventional transmission line.The voltage and current on both sides no longer follow the Kirchhoff law of lumped parameter. In order to solve this problem, phase selection and differential protection based on wavelet transform is proposed. The mode components of the reverse traveling wave and the current of the half wavelength line are transformed by wavelet transform, and the phase selection is carried out according to the results of the wavelet transform. The wave heads of both sides of the mode current after the fault phase wavelet transform are respectively integrated. The differential protection is constructed with the absolute value of the sum of integral current on both sides as the differential current and the absolute value of the integral difference as the braking current. PSCAD simulation proves that the protection method is suitable for half wavelength line, which can accurately partition the internal and external faults, achieve reliable operation in the District, and reliable faults outside the area.