Polymer materials are used in the structural members such as aircraft, ship, automobiles in order to enlarge and lighten the machinery and structures. In such the machinery and structures, the complex destruction phenomena are generating by the deterioration of use conditions of the polymer materials. And the materials are placed under biaxial or multi-axial stress conditions rather than uni-axial stress conditions due to their complicated structures. To understand the basic deformation behaviours and the features in destruction process under multi-axial stress conditions is more important in the reliability and the accident prevention plan. To help overcome this problem, the authors have developed a hydraulic high-speed biaxial loading test device. In this study, we had comparative study for the values of the dimensionless stress intensity factors, F values by the photoelastic and caustics methods to clarify deformation behaviours and characteristics of polymer materials under biaxial stress conditions.