Stress distribution of gray cast iron was analyzed by the finite element analysis based on the actual distribution of graphite flakes embedded in pearlite. Three types of two-dimensional FE-models were used: (1) “true model” where graphite flakes were distributed in pearlite as observed, (2) “voids model” where graphite flakes were replaced by voids of the same geometries, and (3) “single void model” where one of selected voids which showed higher stress in the vicinity of void tip in the pearlite. As the voids model showed higher stress in the vicinity of each void tip, it was concluded that the voids model was appropriate for the safe-side evaluation of gray cast iron strength. Furthermore, a simplified method of strength evaluation was proposed by comparing the results of the voids model with those of the single void model. Since the maximum ratio of the stress near the void tip was 6.27 between the voids model and the single void model, tensile and fatigue strengths of gray cast iron was evaluated by the stress intensity factor multiplied by 6.27 using the maximum length of graphite flakes, the threshold stress intensity factor range and fracture toughness of pearlite about the tested diesel engine cylinder block. The method validated the safety of cylinder block of the tested diesel engine.