The invention discloses a low-voltage phase-change switch automatic phase-change system and method. The system comprises a phase-change switch unit in a phase-change switch type three-phase load automatic adjustment device. When three-phase load imbalance occurs, the phase-change switch unit randomly switches a plurality of phases of which the carried load is larger than set a set value to a plurality of phases of which the load is smaller than the set value according to monitored load conditions; a permanent magnet relay is used as an action element; phase change time is smaller than or equalto 20 ms; and during a phase change process, the interruption of the power supply of a user can be avoided, and the quality of the power supply can be guaranteed. According to automatic phase change,when the three-phase load imbalance occurs, the phase-change switch automatically switches one or more phases carrying large load to one or more phases with small load according to the monitored loadconditions.