Abstract: The ratio of the power spectra of random array to whose unit is called the coherent factor. By analyzing the statistical data experiment of ours, we have studied the fine structures of the curves of coherent factor, introduced a new concept, namely the limited random walk; and found out the formula of the ordered aperture angle for which the values of coherent factor take from N2 to N. This formula has shown that the angle is inversely propertional to the dimension of random array, but is indeperdent of the total number of random points, and that the angle is several times as large as that of the power spectra of regular array in the same domain.