During data sharing process across people, users do not want the information that contains privacy to be shared with everyone else; some people may only want to share it with someone they are familiar with. To solve this issue of privacy preservation in data-sharing applications, we propose a novel user-centric method. Our main contributions include the followings. (1) Users can select key words or characters for their own privacy information, which is a user-centric way to protect privacy. (2) During the process of data sharing, data substitution can be used to ensure privacy preservation as well as high successful rate of data sharing. (3) Our method can be used in different data-sharing applications in a flexible way. Simulation results show that our method can achieve our privacy preservation goal.