The concept of NFV appears to be a promising direction to save cellular network service providers from endlessly increasing capital investment, given the fast evolving mobile broadband communication techniques and unprecedented consumer demand for quality of service and quality of experience in mobile access. Meanwhile, given the deployment of NFV, the virtualized network functions and the physical hardware resources are still vulnerable to natural disasters and malicious attacks. We present in this article the first framework for reliability evaluation of NFV deployment and specific algorithms to efficiently determine the key set of physical or logical nodes there.