Considering the terahertz near-field scattering characteristics, a high-frequency terahertz radar cross section(RCS) measurement system was presented based on a CO2 laser pumped terahertz laser and an independent double-deck rotation platform. The reliability of the system was verified by utilizing stainless steel smooth spheres as the standard calibration targets. The error between measurement result and the theoretical value was less than 3 dBsm and the signal-to-noise ratio is better than 24 dB. For the first time, RCS measurement of metal plates was performed with different materials and coatings, and metal cones with different bottom diameter, at a high frequency of 3.11 THz. The RCS difference of pure, anodized, painted aviation aluminum and P304 stainless steel plates, was demonstrated. The RCS of cones with different bottom diameters made of pure aviation aluminum plate was also compared. This work can lay the foundation for further study of the complex target RCS research in the terahertz band.