The disclosure provides controlling method of MiFi and device thereof. Herein, MiFi is provided with at least two SIM cards of different telecom carriers. The controlling method of MiFi includes: monitoring a currently connected data network corresponding to a SIM card of a source telecom carrier is disconnected; if disconnected, then selecting a SIM card of another telecom carrier except for the SIM card of the source telecom carrier as a SIM card of a target telecom carrier; and connecting to a data network corresponding to the SIM card of the target telecom carrier. In the disclosure, even if MiFi could not continuously access to currently connected data network due to inferior network condition thereof, MiFi still can select and connect to a data network corresponding to a SIM card of another telecom carrier, whereby solving problems that MiFi may be restricted by network condition of telecom carrier to which the inserted SIM card belongs in the prior art and improving user's experience.