The invention discloses a method and a system for realizing context synchronization during idle-state signaling reduction (ISR), wherein the method comprises the following steps that: user equipment (UE) judges whether a state indicator of the UE needs ISR synchronization when executing tracking area update (TAU) or routing area update (RAU), and sets an update type as ISR synchronization in a TAU request message or a RAU request message and instructs a latest accessed user mobility control management entity of the UE if the state indicator of the UE needs ISR synchronization; and the UE requests an accessed user mobility control management entity to update the context thereof by the context of the latest accessed user mobility control management entity of the UE. The method and the system can solve the problem of context synchronization between two user mobility control management entities under radio access technology (RAT).