The invention discloses a switch power supply converter. The switch power supply converter comprises a rectification circuit, a transformer, a first field effect transistor, a second field effect transistor, a first resonant capacitor, a second resonant capacitor, an output circuit, a first resistor, and a second resistor. The transformer comprises a first primary coil, a second primary coil, and a secondary coil. The first primary coil is parallely connected with the first resonant capacitor, and the first input end of the first primary coil is connected with the drain electrode of the first field effect transistor. The second input end of the first primary coil is connected with the positive output end of the rectification circuit. The grid of the first field effect transistor is used to receive a first square wave signal, and the source electrode of the first field effect transistor is grounded. The first output end and the second output end of the secondary coil are connected with the output circuit. The switch power supply converter is advantageous in that the duty ratio of the switch power supply converter is effectively controlled, and the converter works at an optimal duty ratio, and therefore the power supply works in an optimal efficiency range, and the conversion efficiency of the power supply is guaranteed.