Abstract: The active surface control technology has been widely used in the radio telescope which has large aperture and high precision. Actuators in the active surface system compensates the surface precision and radiates electromagnetic wave, which can interfere the observation of radio telescope. Considering the current research status, this paper analyzes the radiation source of an actuator for extremely low electromagnetic radiation requirement. The signal from the actuator’s control board is used to build a math model, crystal oscillator circuit is selected to perform calculation, the parameters of PCB and components are set appropriately, and Ansys software is used to perform finite element analysis on frequency domain, in this way, the result and the rule of radiation are obtained. Finally, the near field test verifies the validity of this method. This method provides a validation way for the optimal design of electromagnetic compatibility (EMC) about the actuator′s control board, and settles the base to reduce the electromagnetic radiation of the active surface system.