With the increasing number of X-band dual-polarization radar networks, making network observation of X-band dual-polarization radars and S-band dual-polarization radars has become more necessary. Based on the observation data of the severe convective weather in Beijing on 27 July 2021, the consistency of polarization parameters between the X-band radar network and S-band dual-polarization radar is quantitatively analyzed. The results indicate that Beijing X-band radar networks and S-band dual-polarization radar have a favorable consistency on reflectivity factor (Z), and the differences of differential reflectivity (ZDR) are concentrated near 0 dB, specific differential phase (KDP) has significant difference in the area where Z≥30 dBz. Based on the characteristics of the observed polarization parameter differences, two fusion mosaic methods of parameters are compared: one is direct fusion mosaic and the other is distance-weighted with an exponent. By analyzing vertical cross-section (VCS) of polarization parameters, we see that the blind area of radars could be made up for each other, and KDP can have a more natural transition through the fusion mosaic method distance-weighted with an exponent. The fusion effect could provide some references for different band radars needing fusion mosaic.