In recent years, with the continuous development of big data, Internet and cloud technologies, the trend of digitalization and informatization of libraries has become more and more obvious, so the services provided to readers are not only borrowing, reading and returning, but also adding personalized services, namely accurate positioning and personalized services of smart libraries. User portrait provides a powerful tool for the library to understand users, gain insight into users, and then realize personalized intelligent services with knowledge, scene and initiative. In this paper, the author will systematically expound the characteristics and requirements of personalized intelligent service in libraries, integrate the application of user portraits into personalized service system, and design a model framework of personalized intelligent service in libraries based on user portraits.