The present invention discloses a mobile telephone address list automatically backing up method and device. Said method includes user setting address list backing up parameter, address list data automatically synchronizing backing up from SIM card to main unit, address list data automatically synchronizing backing up from main unit to SIM card, when mobile telephone starting up, it automatically detecting whether SIM card being replaced, if it is, then prompting user selecting: 1, using SIM card address list covering main unit address list, 2, main unit address list covering SIM card address list, 3, SIM card address list and main unit address list mutually adding, after user selecting to proceed data synchronization. User can set one default address list in SIM card and main unit address list, the subsequent operation all operated in default address list, and automatically backing up modified data to another address list. Said invented device includes setting device, storage device, analytic set, detection device, read-write, and controller. The present invention raises mobile telephone address list data integrality and accuracy.