Abstract: In view of problem that traditional soft start mode of mine-used asynchronous motor has big starting current, small starting torque, and cannot achieve overload or full load start, voltage regulation circuit and protection circuit were improved based on existing grading discrete frequency conversion principle, and an improved soft start mode of grading discrete frequency conversion for mine asynchronous mator was put forward. The main voltage regulator circuit uses gate turn-off thyristor GTO instead of traditional SCR thyristor to adjust power frequency, and uses ideal switch group instead of three-phase circuit breaker to control its turn-off, so as to prevent circuit damage caused by over-voltage or over-current, and achieves purpose of circuit protect. The Matlab simulation results show that improved soft start mode of grading discrete frequency conversion can not only reduce starting current and increase starting torque, but also effectively protect the circuit.