Based on the Schaaff's theory which is established by Van Der Waas's equati
on, a theoretical formula for calculating the third-order nonlinear paramet
er of the organic liquids is derived. By using this formula we calculate th
e values of third-order nonlinear parameter CIA for several kinds of organi
c liquids. The results show that the range of CIA values of the organic liq
uids is about 63 similar to 183.