IN is a significant property in the development of digital media. The demand for IN products and services with good user experiences is increasing in business, consumer market and public sectors. However, the study of design approaches of creating interactive digital narratives with desired user experience is still in its infancy. The project is intended to contribute a better user experience in IN systems from the perspective of user agency. It aims to have a deepened account of the concept of user agency, to investigate how to design the user agency, and to have a better understanding of the relationship between user agency and user experience. The user agency was defined as a satisfying power to be able to conduct the desired actions and cause the expected consequence for a certain intention after a comprehensive literature review on the concept of agency from the perspective of psychology, sociology, neuroscience and digital media in this research. A framework was implemented during the project, which summarized 3 key aspects need to be considered when designing user agency in IN systems: 1) Intention, 2) Action Selection, 3) Outcome Comparison. Approaches of designing user agency were summarized and mapped in the user-centered design process in the framework. The framework was validated by an experiment which shows that the user agency of the IN system redesigned based on the framework was significantly better than the original one without the guidance of the framework. The experiment also found that there is a moderate positive correlation between user agency and user experience.