Abstract: Can't do without the participation and t of the technology of the power from life f our country cwith the developed country. Here, by using the technology, such as advanced electric and electronic technology, it turns the ordinary electricity into the steadily voltage and current output. At first, I will introduce the meaning of the Switch Mode Power Supply, the Switch Mode Power Supply is a Power supply which utilizing modern electric and electronic technolodvanced and low-priced power supply could make the power country catch up with the developed country. Here, I will introduce the ; flyback; PWM