Abstract:  Compared to the conventional array, Each element of the switch antenna array is sampled by a single channel consequently, which not only reduces the hardware cost but also lowers the effects of the differences in gain and phase between the receiving channels on estimation. However, the present researches on the switch antenna array do not take the effects of the switch antenna array’s switch interval on direction finding into consideration. For supplying this gap, at first, referring to the conventional array, the band limit of narrowband signal in the switch antenna array is defined, the relationship between the band limit of narrowband signal and the switch interval is proposed also. Then, by citing the MUSIC algorithm in switch antenna array, both signal band and switch interval are taken into account and the MUSIC algorithm in switch antenna array’s first-order estimation error is deduced theoretically. Finally, the MUSIC algorithm and the spatial FFT algorithm in switch antenna array are simulated with different switch interval. The relationship between the two algorithms’ direction finding error and their switch interval is analyzed. The simulation demonstrates the result of theoretical analysis.