The liquid cell theory can be successfully applied to cholesteric liquid crystals. Using the statistical methods and defining an order parameter tensor　 we ded uce the distribution function and the Helmholtz free energy　 which is the functi on of the order parameter tensor and its derivatives. The expression of the free e nergy we obtain has the same form with of the Landau theory. In a local coordina te system　the long－range orientational parameter Sand the phase－induced biaxiality order parameter are defined. By minimizing the Hemholtz free energy　 we numerically calculate the temperature dependence of Sand .The r esults agree with the experiment.