Abstract:The process of thyristor changing workfrequency of electric power into low intermediate frequency was introducd, which were successfully used in Gongchang double frequency (low intermediate frequency) Quenching machine.In contrast with Belgium OSB double frequency (workintermediate frequency) Quenching machine, Gongchang double frequency (low intermediate frequency) Quenching machine reaches properties of foreign machine; a new homemade path of high-efficiency and low cost is put out.