A new approach to simultaneous acquisition of phase-stepped photoelastic fringes using a CCD camera equipped with a pixelated micro-retarder array is described for the investigation of time-variant problems. This method is applied to the study of quasi-static crack growth in a quenched thin glass plate. The distributions of the principal direction as well as the principal stress difference around a growing crack tip are obtained by the proposed method. Then, not only the mixed-mode stress intensity factors but also the T-stress are evaluated from the distribution of the principal stress difference, and they are validated using the reconstructed phase maps. Results show that the proposed instantaneous phase-stepping technique is effective for the study of the crack growth behavior in a thin glass plate.