The photoelastic method is an experimental technique that combines optics and mechanics for a stress analysis. The photoelastic phase-shifting technique is different from the moiré, holography, and speckle phase-shifting techniques, which only need to measure one parameter. The photoelastic phase-shifting technique needs to assess isoclinic and isochromatic parameters, which affect each other, seriously hindering the development of the phase-shifting photoelasticity method. First, the interaction between the isoclinic and isochromatic parameters is analyzed in detail. Secondly, an algorithm is proposed to adjust the mutation and obtain the correct isoclinic parameter affected by the isochromatic parameter. This method can effectively eliminate the influence of the isochromatic parameter. The isoclinic parameter is consistent with the theoretical value, which verifies the effectiveness of this method. Finally, the photoelastic method uses the proposed algorithm to test the stress at different positions of the turbine blade root. Moreover, the bearing capacity of the turbine blade root is analyzed to provide support for the safe use and optimization design of the turbine.