For study the characteristics of terahertz radar scattering cross section, by building a low-frequency terahertz radar test system, and with the help of standard target method, experiments and research work about terahertz radar scattering cross section of rough aluminum plate were carried out. The experimental results show that: In the small angle scattering, terahertz radar scattering cross section changes much obviously with the increase of the scattering angle; But when the scattering angle is more than 5°, terahertz radar scattering cross section varies with the scattering angle tends to be slow; And when the scattering angle is more than 12°, the detection signal strength attenuation cannot be measured. The phenomenon that microwave radar scattering cross section size changes with the angle of scattering while acuteness oscillation does not appear in the testing of terahertz radar scattering cross section. Comparison of the test results with the same size of microwave and laser radar cross section, it can be the concluded：In the vicinity of 0°, themagnitude of terahertz radar scattering cross section is two orders lower than the same size microwave radar scattering cross section, but is an order higher than the same size laser radar scattering cross section.