The formation mechanism of the antenna's transmitting and receiving patterns was particularly analyzed for the study of the reciprocity between transmitting and receiving patterns when the antenna polarization mismatched. The main factors affecting the transmitting and receiving patterns were presented as follows: current element directivity, current distribution and phase difference formed by wave path difference. The polarization matching factor was deduced for the analysis of the polarization mismatching between transmitting and receiving antennas. And the two definitions of polarization matching factor were compared. The results show that the differences between the two definitions depend on whether the primary element directivity is assigned to the polarization matching factor or not. If it is, the transmitting and receiving patterns are not equal; otherwise, the transmitting and receiving patterns are equal.