A serious of factors influencing tag antenna's radiation efficiency was analyzed. The influence of conductive ink layer thickness on RFID tag antenna's radiation efficiency was studied using dipole and bow-tie antennas as object. The results showed that the factor influencing antenna's radiation efficiency is the total amount of conductive ink used, not how it is distributed throughout the structures. The purpose was to provide guidance for control and improvement of the conductive ink in actual production of RFID tag antennas.