The invention discloses a structure for a switch power supply circuit, which has the effects of low cost and short design period. A structure for the switch power supply circuit comprises a power chip (U18), a filter rectifier circuit, a high-frequency transformer (T1), a rectifier filter stabilized voltage output circuit, a feedback bias circuit, a photoelectric coupling circuit (19) and the like, the primary side of the high-frequency transformer (T1) is connected with the power chip (U18), the auxiliary side of the transformer acquires a high frequency rectangular wave voltage under the self-starting action of the power chip (U18), then a stable direct current voltage is obtained through the rectifier filter stabilized voltage output circuit, the feedback bias circuit takes a voltage sample from the output voltage, a voltage signal is converted into a current control signal through the photoelectric coupling circuit (19) and is inputted into a current control end of the power chip (U18), a sampling resistor in the power chip (U18) takes a voltage sample, finally an internal comparator and an oscillator work together to implement pulse width modulation, and an internal switch tube is triggered to conduct at the frequency of a certain duty ratio.