Abstract: Rheological parameters of drilling fluid and selection of rheology pattern play an important role in drilling operation. Using exhaust algorithm and other methods, such as numerical computation method, regression analysis and optimization theory, three evaluation indices, i.e., correlation index, sum of squares of residues and variance of residues are introduced. Using golden section method, the contraction of the root interval can be accelerated. These studies give birth to the so called improved golden section method. In this improved golden section method, initial iterative values become unnecessary, and the method has good convergence, getting rid of deficiencies of the rheological model presently in use. This method is suitable for the parameter calculation and optimization of rheological patterns using 2-parameter, 3-parameter and 4-parameter equations. Using computer language MATLAB, large scale computation can be realized. Comparison of the computation results and those of others shows that the three evaluation indices presented are useful, and when used in combination with the improved golden section method, rheological parameters can be calculated, and rheological model optimized with good accuracy. The computational result of the variance of residue is reduced by 19.7%, a higher computational accuracy.