Public library credit service is a new way of service carried out in the field of public library in China within these recent years. Library resources and services could be used by users through their social credit index directly exempt from their library cards and deposit. Although library credit services are different from traditional forms of service, it is not creation, only a new way of service and a transcendence of traditional service. The establishment of the user credit system or the combination with the social credit institutions is the basis for the development of credit services in the library. Library credit service is one of the important means to improve the effectiveness of the library services, and integrated innovation and social participation are the guarantees of the realization of the library credit service. The alliance and standardization are the future directions of the library credit service.