While many research projects in the world have been addressing challenges posed by digital preservation, digital libraries in China have their own native problems that have never been addressed before. Similar problems may occur in other countries, and their memory institutions may be less prepared to handle them. Quite often, information in the native special digital objects is also unique in world and requires more precise preservation. This paper analyses the requirements and challenges of digital libraries in China and describes a practice of sustainable preservation risk management method based on web service technology. This system demonstrates an architecture that provides a minimal approach to handle the native problems, which can be easily ported to similar situations. It also provides a way to leverage the existing tools/services. And to mitigate the lack-of-professionals problem in digital preservation, multiple preservation risks are managed, which can help schedule the preservation actions efficiently.