Abstract: The spatial polarization characteristics of dual-polarized arrays and its influence on the polarization scattering matrix measurement of target are analyzed in this paper by using crossed dipoles as elements.Because of the nonorthogonality of the radiated electric field at off-broadside, it is inevitable to cause cross-polarization interference between crossed dipoles.The cross-polarization characteristics of crossed dipoles are analyzed according the traditional evaluation definition.Furthermore, the cross-polarization isolation (XPI) of dual polarized radar system is defined in the respect of target polarization scattering matrix measurement, which is denoted by the polarization measurement formula and evaluate the stability of polarization measurement methods.