A method, an apparatus, and a system for a location update are provided. When detecting that a location update needs to be performed in a first mobile communication network, a request message including instruction information is sent to a mobile management device in the first mobile communication network, so that the mobile management device in the first mobile communication network sends a request message to a mobile management device in a second mobile communication network when executing the location update, so as to trigger the mobile management device in the second mobile communication network to reset a periodic update timer, which implements that a location update of a single-card dual-standby user equipment is synchronously performed in the first mobile communication network and in the second mobile communication network.