The progress of rheological testing methods has promoted the researchers' understanding of viscoelastic fluids in a wider testing range. The polymer solution used for oil displacement has the characteristics of “Three-stage” rheological curve （zero shear section

shear thinning section

and ultimate shear section）

so a more accurate description model and limiting conditions are extremely needed. Taking partially hydrolyzed polyacrylamide and hydrophobically associating polymer as the research objects

the rheological curves in a wide range （0.01 ~ 10 000 s

-1

） have been analyzed

and the changes of viscoelastic modulus have been studied. The results show that under the experimental conditions

the rheological curves of the two polymers can be described by Carreau rheological model. The structural viscosity formed by hydrophobic association greatly enhances the elasticity of the solution

and makes the elastic modulus of the polymer P-P4 dominant. Considering the influence of elastic characteristics on the rheological curve

the relaxation time spectrum derived from the experimental data of small amplitude oscillation is used to limit the characteristic relaxation time（

λ

）. Finally

the experimental data are highly matched by the nonlinear regression fitting curve of Carreau rheological model. When studying the rheological constitutive equation of viscoelastic solution

it is necessary to fully consider the solution characteristics

establish the relationship between different test parameters

and establish reasonable limiting conditions

which are effective means to optimize and improve the rheological constitutive equation of viscoelastic fluid.