The phase difference measurement accuracy for the channels receiving signals in the interferometer is discussed. After the limitations of the traditional formula are pointed out, a theoretical computation formula of the standard deviation for the phase difference measurement error of the channels receiving signals in the interferometer is proposed by using the signal energy SNR (Signal-to-Noise Ratio) instead of the in-band power SNR. In theory, the universality of the formula is proved from the point of view of demodulation and match filtering. And the correctness of the theoretical analysis is verified by the simulation for various modulated signals and pulse series signals. It reflects that the standard deviation of the phase difference measurement error for the channels receiving signals in the interferometer is inversely proportional to the square root of the signal energy SNR. This theoretical result provides a general guidance for the computation, demonstration and analysis of direction finding accuracy index in interferometer engineering application.