This paper being introduced to the circuit design of over2voltage, under 2 voltage, and delay p roduction and the operating p rincip le. This protection circuit has many advantages such as over2voltage p rotection, under2voltage protection,wide protection range, adjustable delay time, sensitive protection action and so on. It can be widely used as a protector in the event of over 2 voltage, under 2 voltage and the other abnormalworking conditions.