Materials samples of some common military coating including radar absorbing coating， high emission infrared coating， radar absorbing and high emission infrared compatible coating， radar absorbing and low emission infrared compatible coating， and aviation anticorrosive coating are prepared and their emissivity at different observation angles in Ka band is measured in this paper. An improved measurement scheme based on voltage method is proposed and used for the measurement experiments， The measurement scheme can eliminate the errors caused by antenna sidelobe and thickness difference between sample and reference bodies. In addition， the main sources of measurement uncertainty are analyzed and discussed.