It is now a basic premise to acquire the polarization scattering matrix of radar target accurately before the polarization information processing. Based on a pair of linear frequency modulation signals with opposite slopes and aimed at the simultaneous polarimetric radar adopting the digital dechirp processing, the mathematical model of the influence of the intermediate frequency deviation and sampling frequency deviation on simultaneous polarization measurement was derived. An intermediate frequency deviation and sampling frequency deviation joint estimation and calibration algorithm was proposed. Simulation and real data results show that the radar frequency stability can change the peak position and phase of the simultaneous polarization scattering matrix measurement. The approach proposed can regulate the peak deviation effectively, compensate the phase error and accurately acquire the four elements of polarization scattering matrix.