In recent years, the functionality of smartphones has been rapidly improved, then, the smartphones are not only used for telecommunication but also for various applications, such as email and social network accessing. These applications raise new security issues to smartphone users, however, the current protection mechanisms of smartphones are not sufficient due to convenience issue and shoulder-surfing issue. We therefore propose a non-intrusive authentication approach based on touch screen of smartphones. To the best of our knowledge, this work is the first publicly reported study that adopts the histogram features of touch screen to build an authentication model for smartphone users. Our empirical results for fifty-five participants show that the proposed approach is feasible. The performance of the proposed approach could be increased if users continuously operate their smartphone after a period of time. Finally, we further discuss the applications and limitations of the proposed approach.