The fatigue life in arc welded parts of the chassis component of SAPH45 steel in automobile is affected by various defects and residual stress due to welding. Moreover, it is hard to measure directly the crack initiation length of the welded part in chassis component due to the complicated geometric shape. Therefore, to assure the safety of vehicles, it is necessary to evaluate the crack initiation life by using a non-destructive technique (NDT). In this study, the acoustic emission measurement was adapted to monitor the crack initiation of the welded part during the fatigue test. The crack initiation length was verified by a computerized image processing system under stroboscopic light illumination. Besides, to consider the variation of fatigue data, the crack initiation life was statistically evaluated.