In recent years, the X-band dual-polarization phased array weather radars (X-PAR) have been densely deployed in multiple regions across China, for they have the advantage of high spatio-temporal resolution. However, the data quality and limited coverage of a single X-PAR restrict the data application. To give full play to the dense radar network composed of the S-band dual-polarization weather radar (S-POL) and X-PAR, and to obtain precise three-dimensional observation results, this study constructs the data quality evaluation parameters for the radar variables with different wavelengths to achieve the interpolation and mosaicking of single-wavelength radar networks. Furthermore, the S-POL mosaic is taken as a background field with the low-resolution and credible characteristic, and combined with the observed detail structures from the X-PAR mosaic, the fusion of the S-POL and X-PAR radar mosaics is realized. The results show that by calculating the data quality evaluation parameters, combining the spatial distance from radar bins to grid points, and setting weights to perform interpolation and mosaicking for each radar, the mosaics can retain the high-quality observations and common observational characteristics of the radars. With the fusion method of the S-POL and X-PAR radar mosaics simultaneously, the retention of the intensity distribution of the S-POL and the detailed features of the X-PAR is achieved. This method can effectively help utilize the observational advantages of the densely networked S-POL and X-PAR and obtain an accurate and detailed three-dimensional radar observation field.