Abstract: This work aims at sparse array without grating lobe for passive sonar, in order to increase frequency of the passive sonar and reduce the cost. According to traditional method, the distance between two contiguous sensors in sonar array should be less than the wavelength of highest frequency of the signal, otherwise the grating lobe appears on directivity pattern. The paper realizes that the conclusion of the grating lobe emergence it is not fit to the passive sonar due to the sine wave signal model in traditional method, in fact the input of passive sonar is random signal. The model of Gauss random process is fit to passive sonar which is used in this paper. Prom three aspect of the computer simulation, theory analysis and real passive sonar signal, it is revealed that the grating lobe do not appear on beam pattern when the distance between two contiguous sensors in passive sonar array is longer than wavelength of highest frequency if the signal band is wider than 1 oct. Whitening of the radiated noise can widen the frequency band, to ensure the beam pattern without the grating lobe. The conclusion is that the wavelength of signal can be shorter than the distance between two contiguous sensors without grating lobe if the band of radiated noise is wide enough.