This paper describes a new four parameter method of analysis for determining of the stress intensity factor (SIF). The method bypasses the error-prone measurements on the isochromatic pattern near to the crack tip and uses data from the
near of the crack tip as well as extended stress field. Suitable expression was developed for the determination of the fourth parameter based on isochromatic fringe loop information. Results were obtained by the computer program (EGYPT) for different values of the parameters β and α to give the best accuracy of determining the stress intensity factor (K). The results obtained for Dobeckote-505 show good agreement with the analytical results.