A software upgrade method and system for a mobile terminal includes locating partition tables of a new version of software and an old version of software, generating a corresponding backup list, scanning all files of the new version of software, generating a differential upgrade package that comprises a partition table of the new version of software and the backup list, saving backup data, to be backed up in the mobile terminal, into a SD card according to the backup list, re-partitioning a mobile terminal memory according to the partition table of the new version of software in the differential upgrade package, correspondingly writing the backup data on the SD card into the partition, decompressing the differential upgrade package to obtain a corresponding differentiating file, generating corresponding new version files according to the differentiating file and the old version files in the mobile terminal, and writing into the mobile terminal.