An expression concerning the variation of the pitch of SmC* liquid crystals is obtained by using the cell model in statistical mechanics with the introduction of the distribution factor ζχ of the chiral centers in the interaction potential between biaxial molecules containing multiple chiral centers.It shows the condition for inversion of helicity of the liquid crystals.With proper choice of the values of parameters involved we have calculated the variation of the pitch with temperature for liquid crystals TDOBAMCC,FLC,PACMB and H6/10.The calculated results agree well with the experimental data.