In this paper, the calculating course of the plane-wave algorithm is introducedto solve the sound wave equation and the band structure of phononic crystals. The phononic crystals of two-dimensional binary liquid systems are studied. In conclusion, the CCl4/mercury system is easier to obtain the band-gap than the mercury/CCl4 system. With the increase of the filling fraction(f), the width of the band-gap becomes wider and then narrower. The widest band-gap of CCl4/mercury system appears at f=0229,where ΔΩmax=0549.While the width of the band-gap in mercury/CCl4 system increases consistently with the filling fraction, when f=0.554,ΔΩmax=0515.Under the same filling fraction, the variation of the cylinder diameter and lattice constant does not affect the band-gap width ΔΩ.