Abstract: To obtain high-quality compact polarimetric (CP) synthetic aperture radar (SAR) data, internal calibration is used to monitor amplitude and phase variations within the radar system during imaging, while external calibration is required to analyze and compensate for errors in the transmit-receive (T/R) link. This paper proposes an external calibration method for circular transmit and linear receive (CTLR) mode compact polarimetric SAR based on active radar calibrators. The method requires only three active radar calibrators with different polarization scattering characteristics to achieve unbiased estimation of the system polarization distortion parameters, featuring closed-form analytical solutions along with simplicity and high efficiency. Simulation results demonstrate that all four calibrator combination schemes included in the proposed method can achieve high-precision calibration under the influence of noise and inherent calibrator errors, thereby validating the correctness of the presented method.