In the paper

we took the xanthan gum

which is widely used in the oil-recovery industry as the"fracturing fluid"

as an example and analysed the mechanism of its gelling. Introducing the adsorption reaction and thixotropic function f (t) into the molecular network model and assuming the contribution of the broken pieces of network

the free and stray chains to the toatl stress tensor to be Newtonian

we obtained a constitutive equation on the basis of the carreau-Bird model. The

parameters in the constitutive equation were estimated and optimized according to the experiments data of the linear viscoelasticity and non-linear material functions of the xanthan gum by using the tolerable multi-surface-body gradient method with constrain-ed conditions. This model can predict the rheological properties which are in agreement with those of the xanthan gum. It is obviously found that the shear viscisity and complex one of the xanthan gum do not obey the Cox-Merz rule in the range of shear rates of these experiments.