The hot sheet formability test machine and the grid measurement and analysis system were used to determine the forming limit diagram (FLD) of AZ31 magnesium alloy sheet in the forming temperature range of 150~250 °C. The deep drawing processes were simulated using DYNAFORM with the FLD and Keeler’s function as broken criterion respectively in the forming temperature range of 150~250 °C. In order to validate the simulated results, the deep drawing tests were also performed. The results show that breaking can be predicted more precisely in the forming process using the FLD as the broken criterion than using auto Keeler’s broken criterion when simulating with DYNAFORM