Although the convenience of drivers is maximizing due to the full-fledged self-driving service, complex problems are still emerging in various areas, including legal, ethical, and social aspects. As a result, social awareness and acceptability of self-driving cars have not been sufficiently formed, and efforts to improve stability are essential at this point. Therefore, in this study, only records of accidents while driving autonomously were selected among the accident data of autonomous vehicles provided by California DMV and the causes of accidents were analyzed for about 400 cases. As a result, main causes were verified as low recognition rate of parked vehicles, inability to grasp changes in vehicle size due to attachment of convenience goods, insufficient defense driving system, low recognition speed in special road conditions, etc. To mitigate these problems, it is expected to increase vehicle recognition rate, reconstruct safety area range, devise additional vehicle functionalities for defensive driving, and emphasize the importance of communication between self-driving cars and smart roads. These measures aim to enhance the safety of autonomous vehicles and contribute to increasing positive social perception and trust in autonomous driving.