The peak value and Full Width at Half Maximum(FWHM) of scattered light's spatial spectrum intensity distribution of air bubbles in water can be used to determine bubbles'size and density. By the developed air bubbles producing setup and scattered light's spatial spectrum intensity measuring and analyzing system,how detecting distance affects backward scattered light's spatial spectrum intensity was investigated experimentally. The experiment results show that as air bubbles'size and density are invariable,the change of detecting distance has different effect on the peak value and the FWHM of scattered light's spatial spectrum intensity distribution under different illuminations. The peak value and the FWHM of scattered light's spatial spectrum intensity distribution are unchanging as the detecting distance increases under expanded beam illumination,for the number of bubbles scattering light increases constantly,which can offset scattered light intensity's losing caused by a longer distance propagation. But the.peak value reduces gradually and FWHM increases as the detecting distance increases under the slim beam illumination. The experiment results also show at slim beam illumination has advantage for long distance detecting.