Photoelastic stress analysis has been used to determine stress intensity factors for two types of models (C-R and L-R) with two cracks at outer surface of cylindrical pressure vessel. The crack geometry is a portion of a circular arc. Analysis method used in this paper involves a Taylor series correction for the maximum in-plane shear stress and does not involve stress separation, which is proposed by C.W. Smith, et al. Results were qualitatively compared with the theoretical results derived for the one outer crack and the two inner cracks in internally pressurized cylinder by A.S. Kobayashi, et al. and by R.J. Clifton, et al. respectively. It is shown that the obtained data are consistent with the theoretical results and the Smith's method can be reasonably applied to three-dimensional crack problem in photoelasticity method.