Abstract: Polarimetric interferometry SAR (PolInSAR) coherence is important information when solving the coherence optimization problem such as when executing forest parameter inversion. The distribution of coherences, the set of coherence with different polarimetric bases, is related to the field of values in a complex coherence matrix. It is discussed the specialty of the field of values of complex coherence matrix with different formation, and the relationship between the coherence with different polarimetric states and the field of values of complex coherence matrix. Using simulated SAR data and real SAR data, the influence of the sizes of window and scatters type on the field of values of a complex coherence matrix are evaluated. The results indicate that the field of values of coherence matrix can provide a new method to obtain optimal polarimetric bases and optimal coherence.