It is necessary to calibrate polarimetric synthetic aperture radar (PolSAR) data in order to use the data for science applications. In this letter, we propose an improved algorithm to estimate the calibration parameters based on the Ainsworth algorithm and the Quegan algorithm. Since there is no approximation in the process of the parameter estimation, this algorithm can accurately solve all parameters, even if the crosstalk is high. To verify the effect of the proposed calibration algorithm, this letter analyzes the accuracy of the proposed algorithm with the simulated PolSAR data and Chinese airborne X-band PolSAR data. The results confirm that the proposed algorithm can provide a more stable and accurate solution to the crosstalk parameters.