Dual polarization technology is gradually promoted in our country after Doppler weather radar network. It extends the capabilities of conventional Doppler radar, and can directly detect the differential reflectivity factor and the zero-lag correlation coefficient and so on which are related with the micro-physics characteristics of precipitation. Considering that small error may lead to erroneous judgments when identify the particle phase state with the zero-lag correlation coefficient for its values is close to each other at different phase states and is between0 and 1, the error mean value and mean square root of the zero-lag correlation coefficient are deduced at alternative transmission mode, and each parameter’s effect to the precision is analyzed. It not only provides a useful polarization variable for better identifying hydrometer phase state and clutter recognition, but also provides an practical way to estimate the zero-lag correlation coefficient and relevant. Dual polarization technology is gradually promoted in our country after Doppler radar radar, and can directly detect the differential reflectivity factor and the zero-lag correlation coefficient and so on which are related with the micro-physics characteristics of precipitation. Considering that small error may lead to erroneous judgments when lead the particle phase state with the zero-lag correlation coefficient for its values ​​is close to each other at different phase states and is between 0 and 1, the error mean value and mean square root of the zero-lag correlation coefficient are deduced at alternative transmission mode, and each parameter’s effect to the precision is analyzed. It not only provides a useful polarization variable for better identifying hydrometer phase state and clutter recognition, but also provides an practical way to estimate the zero-lag correlation coefficient and relevant.