The invention discloses a duty ratio control circuit and a control method for a CT power-taking power supply. The duty ratio control circuit comprises a PWM circuit, wherein the output ends of an input voltage sampling circuit, an output voltage sampling circuit and an output current sampling circuit are connected with the analog quantity input end of a microcontroller through a wire; and the output end of the microcontroller is connected with the switch control end wire of the PWM circuit through a wire. By adoption of the duty ratio control circuit and the control method, the following problems existing in the prior art can be solved: the obtained energy by a high-voltage power-taking method cannot be transmitted to a lower-voltage end, so that many limitations in use are caused; the power obtained from an overhead anti-thunder grounding line is unstable and weak; if the power needs to be increased, the weight of the power-taking iron core needs to be increased as well, so that the safety of the power transmission line is affected consequently; when the CT operates in the alternating current, the power supply has quite high fluctuations; if the energy storage function of the rectifying capacitor is implemented, the time constant of the control system is quite high; and various kinds of shortcomings and technical problems, such as a complicated system, high requirement on hardware, low tracking speed, high perturbation and the like, exist in the CT power-taking technology when the current common algorithms, such as a perturbation and observation method, a conductance increment method, a fuzzy logic control method and the like, are adopted.