With more and more users using different devices, such as personal computers, iPads, and smartphones, they can access OPAC (online public access catalog) services and other digital library services in different contexts. This leads to the phenomenon that user's behavior can be transferred to different devices, which leads to the richness and diversity of user's behavior data in digital libraries. A large number of user data challenge digital libraries to analyze user's behavior, such as search preferences and borrowing habits. In this study, we study the user's cross-device transition behavior when using OPAC. Based on the large-scale OPAC transaction log, the online activities between device transitions in the process of using OPAC are studied. In order to predict the follow-up activities that users may take, and the next device that users may use, we detect features from several perspectives and analyze the feature importance. We find that the activity and time interval on the first device are more important for predicting the user's next activity and the next device. In addition, features of operating system help to better predict the next device. The next device used is more likely to predict the next activity after the device transition. This study examines the cross-device transition prediction in library OPAC, which can help libraries provide smart services for users when accessing OPAC on different devices.