A charging method, a network device, and a system, where the method includes performing, by a policy and charging enforcement function (PCEF), online charging for user equipment (UE), switching, by the PCEF, the UE from online charging to offline charging, and starting an offline timer when an online charging system (OCS) is unavailable, and restoring, by the PCEF, the UE from offline charging to online charging when the PCEF learns, before the offline timer expires, that the OCS becomes available. Hence, after a user is switched to offline charging, an online charging function can be recovered in a timely manner when the OCS becomes available. In this way, a user account overdraft risk possibly existing in an offline charging process is mitigated, and deactivation of the user can be avoided in the solutions, thereby improving user experience.