Accurate measurement of differential reflectivity (〖WTBX〗Z〖WTBZ〗DR) of meteorological targets is an important part in the upgrade of the operational China New Generation Weather Radar with dualpolarization capability. The principles of ZDRcalibration methods using external instrument, internal test signal, sun and drizzle are introduced respectively. Key factors that affect 〖WTBX〗Z〖WTBZ〗DRmeasurement accuracy are analyzed, which include drifting biases induced by transmitter, receiver and azimuth rotary joint. In addition, advantages and disadvantages of various calibration methods are compared. Taking the Cband dualpolarization radar operated by Nanjing University as an example, 〖WTBX〗Z〖WTBZ〗DR bias measurements by using external instrument, sun and drizzle methods are presented and analyzed. It is found that the measurements of the three methods have good consistency. Besides, it is also shown that 〖WTBX〗Z〖WTBZ〗DR measurement result changes with azimuth regularly. Therefore, with the long term operation of dualpolarization weather radar, the effect of azimuth rotary joint should not be neglected. The results have a certain reference value for the operation and network observation of dual polarization radar in China in future.