Customary Radar Cross Section(RCS) measurement using far-field or compact ranges is limited due to an increasing difficulty to produce plane wave illumination as the frequency grows higher. An image-based technology for predicting far-field RCS from monostatic near-field measurement is developed. Furthermore, RCS estimation accuracy is improved by decreasing the background noise of the target zone, such as trestle table. At last，sample data sets of 0.14 THz target echo are collected to produce P-band RCS of aircraft carrier.